A.  Introduction

1  Full protection and security (‘FPS’) as a standard of treatment of aliens can be traced back to the customary international law related to the treatment of aliens in international law. In the past decades, FPS has mostly been relevant and applied by arbitral tribunals in the context of international investment law (Investments, International Protection; International Investment Arbitration). It is a standard of treatment which one regularly finds in international investment agreements (Investments, Bilateral Treaties).

2  The traditional understanding of FPS requires States to offer aliens and their property a certain degree of protection from physical injury, caused either by the State or by private parties (see also Property, Right to, International Protection). Applied in the context of investor-State relations, the obligations of States are owed to foreign investors and their investments. FPS not only requires preventive action from the States, but also entails reactive action. Certain case law in the context of international investment law suggests that the FPS standard’s scope of application extends to legal protection and security as well.

3  FPS, unlike other standards of treatment, is assessed by reference to a due diligence standard when the acts complained of are acts of private parties. A State has no strict liability for the harm caused by the acts of private parties.

4  Despite the ancient roots of FPS, contemporary practice in international investment law shows that several features of FPS are still subject to debate, such as the connection between FPS and the international minimum standard (‘IMS’; Minimum Standards) and the fair and equitable treatment (‘FET’) standard of treatment, the extension of FPS to legal protection and security, and the question whether the due diligence standard allows for the taking into consideration of the specific economic and political situation of the State allegedly responsible for the breach of the standard.

5  After discussing the notion, historical roots, and evolution of FPS (Section B), this entry will first briefly discuss the relevance of the standard in contexts other than international investment law (Section C). Subsequently, this entry will focus on the relevance and application of FPS in international investment law. It will first look at how FPS has been formulated in international investment treaties (Section D), to then focus on the link between FPS and the IMS and FET standards of treatment (Section E). The entry will next discuss the scope of application of FPS, first in relation to the authors of the acts complained of (ratione personae) (Section F) and subsequently in relation to the types of acts covered by FPS (ratione materiae) (Section G). It will then discuss the application of the due diligence standard and the question of whether it allows for the taking into consideration of the specific economic and political situation of the State allegedly responsible for the breach of the FPS standard (Section H). The final section (Section I) will state the conclusions of the entry.

B.  Notion, History, and Evolution

6  In addition to its contemporary relevance in the specific context of international investment law, the duty to protect the security of aliens and their property from acts of third parties in their territory has long been accepted in international law (Pisillo-Mazzeschi [1992] 25 ff; Sornarajah [2021] 459). The FPS standard of treatment, as understood in contemporary investment law, has close connections with the responsibility of States for private actors and the accompanying duty of States to act in due diligence to protect aliens within their territory (see Rajput [2020] and ILA Study Group on Due Diligence in International Law ‘First Report’ at 2; International Law Association [ILA]).

7  While some authors have traced the standard’s history to ancient Greece and Rome (see generally, Junngam [2018]; and Ryk-Lakhman [2019] 265), the FPS standard of treatment has mostly become relevant through its inclusion in treaties of friendship, commerce and navigation (‘FCN Treaties’), and the case law of mixed claims commissions in the late 19th century and the early 20th century.

8  The customary norm of FPS has been described as encompassing the obligation of States to prevent acts of individuals that may harm the security of aliens and their property, the obligation of States to apprehend and bring to justice those responsible for injuries caused to aliens, and the obligation for States to possess and make available to aliens a judicial and administrative system capable of preventing harmful acts, and of punishing and apprehending those responsible for such acts (Pisillo-Mazzeschi [1992] 25 ff).

9  These principles have been affirmed in the decisions of several claims commissions established in the late 19th century and early 20th century, and have been applied in cases of occasional acts of third parties (eg HG Venable [USA] v United Mexican States [1927]; Laura MB Janes [USA] v United Mexican States [1925]; George Adams Kennedy [USA] v United Mexican States [1927]), in situations of public disorder, revolts, and violence (eg British Claims in the Spanish Zone of Morocco [United Kingdom v Spain] [1925]; Thomas H Youmans [USA] v United Mexican States [1926]), and in case of civil war or international armed conflict (eg Sambiaggio Case [Italy v Venezuela] [1903]; Armed Conflict, International; Armed Conflict, Non-International).

10  FPS, sometimes under slightly different formulations, has frequently been inserted in FCN Treaties (eg Art. III USA–Nicaragua FCN Treaty of 1956), and was also included in certain draft conventions on foreign investment, such as the 1959 Abs-Shawcross Draft Convention on Investments Abroad (Art. I). The FPS standard of treatment has subsequently been included in bilateral and multilateral investment treaties.

11  In contemporary international law, FPS is mostly relevant as a standard of treatment in international law and international investment law. FPS is an absolute standard of treatment that requires certain treatment to be afforded to foreign investors independent from the level of treatment that is offered to nationals or other foreign investors. While FPS contains both the term ‘protection’ and ‘security’, FPS often is considered to be a unitary concept, which implies that ‘protection’ and ‘security’ are interpreted and applied conjunctly (Reinisch and Schreuer [2020] 545).

C.  Application and Relevance in General International Law

12  The application and practical relevance of FPS outside of the specific context of international investment law have overall been rather limited. Although FPS is firmly grounded in customary international law, there have over the past few decades been very few cases in international law that have applied FPS in other contexts. The few cases in which the standard has however been applied have been based on FPS clauses contained in FCN Treaties.

13  A first example is the decision of the International Court of Justice (ICJ) in the United States Diplomatic and Consular Staff in Tehran Case (United States of America v Iran) (1980) (‘Tehran Hostages’). While the decision mostly revolved around other questions, the case did briefly touch upon the application of the FPS standard. The Court applied Art. II (4) Treaty of Amity, Economic Relations, and Consular Rights of 1955 between Iran and the United States, which contained the following FPS clause:

This clause was applied in relation to two private United States nationals who had been seized as hostages by the invading militants (Tehran Hostages para. 50).

14  A second case before the ICJ which has discussed the FPS standard is the Elettronica Sicula Case (1989) (‘ELSI case’). The ELSI case was brought by the United States against Italy, the former acting in diplomatic protection of two US corporations, which wholly owned the Italian corporation Elettronica Sicula SpA (‘ELSI’). The claims related to alleged violations of the 1948 Treaty of Friendship, Commerce and Navigation between the United States of America and the Italian Republic. Amongst others, the US claimed that Italy had breached the FPS clause contained in Art. V (1) and (3) of the Treaty. In relation to alleged violations of this article, the US had argued that, following the requisition of the ELSI plant by the Mayor of Palermo and the occupation by ELSI’s employees of the premises, Italy had ‘made no effort to prevent or to end it, or otherwise to protect the premises’ (ELSI case para. 105). The Court considered that the FPS standard ‘cannot be construed as the giving of a warranty that property shall never in any circumstances be occupied or disturbed’ and held that in this case ‘the protection provided by the authorities could not be regarded as falling below “the full protection and security required by international law”’ (para. 108). In relation to the claim that the administrative appeal had taken 16 months before being decided, the Court noted that ‘[i]t must be doubted whether in all the circumstances, the delay in the Prefect’s ruling in this case can be regarded as falling below that standard’ (para. 111).

15  Aside from the cases before the ICJ, the FPS standard has also been applied by the Iran-United States Claims Tribunal (‘IUSCT’). In several cases, the IUSCT applied the same 1955 Treaty of Amity, Economic Relations and Consular Rights between Iran and the US, which was applied by the ICJ in the Tehran Hostages case discussed above. In Rankin v Islamic Republic of Iran (1987), for example, the claimant alleged that certain statements attributable to Iran could have had resulted in his alleged wrongful expulsion from Iran as well as damage to his property. Since the Tribunal found that the claimant had failed to satisfy the burden of proving that the statements were a substantial causal factor in his expulsion from Iran or that his expulsion from Iran was caused by specific acts or omissions of Iran, or attributable to Iran, the claims were dismissed.

16  In Emanuel Too v Greater Modesto Insurance Associates and the United States of America (1989), the IUSCT was confronted to a claim by an Iranian national that his property in the US, which had been destroyed by fire (arson), had failed to receive the necessary police protection, and that the US authorities had failed to properly investigate those responsible for the arson. The IUSCT confirmed that States incur responsibility ‘when police protection falls below a minimum standard of reasonableness’, which ‘depends on all the circumstances, including the State’s available resources’ (para. 22). The Tribunal in casu did not find that the claimant had shown that US authorities had failed to exercise due diligence in the protection of his property, or in the investigation subsequent to the destruction of his property (para. 23).

D.  Full Protection and Security in Contemporary Investment Treaties

17  FPS is a standard feature of international investment treaties (Reinisch and Schreuer [2020] 542). The formulation of the FPS standard of treatment however varies across investment treaties. While some investment treaties contain no FPS clause (eg Burkina Faso–Benin BIT [2001]), most treaties use the standard formulation of ‘full protection and security’ (eg Angola–UK BIT [2000] Art. 2). Other treaties instead refer to ‘constant protection and security’ (eg BLEU–Gabon BIT [1998] Art. 3), ‘the most constant protection and security’ (1994 Energy Charter Treaty Art. 10), ‘protection and security’ (Germany–Pakistan BIT [1959] Art. 3), ‘full physical protection and security’ (eg Netherlands–Burundi BIT [2007] Art. 3 [‘sécurité et protection physique intégrale’ in the original text]), or ‘adequate protection and security’ (eg OIC Investment Agreement [1981] Art. 2).

18  Some investment treaties moreover use formulations connecting FPS to international law (eg Germany–Benin BIT [1978] Art 3). Certain recent treaties specifically connect FPS to customary international law. Article 9.6 Comprehensive and Progressive Agreement for Trans-Pacific Partnership (‘CPTPP’; [2018]) thus provides

An almost identical provision can be found in Art. 14.6 Agreement between the United States of America, the United Mexican States, and Canada (‘USMCA’; [2020]).

19  The precise link between FPS clauses and (customary) international law will be discussed in Section E below.

20  Other treaties include references to the fact that FPS standard does not apply to ‘measures necessary to maintain public order’ (eg Benin–BLEU BIT [2001] Art. 3 (2)), or connecting FPS to national treatment (National Treatment, Principle) and most-favoured-nation treatment (Most-Favoured-Nation Clause) (eg Iran–Poland BIT [1998] Art. 4 (1): ‘Investments of national and legal persons of one Contracting Party effected within the territory of the other Contracting Party shall receive in the other Contracting Party full legal protection and fair treatment not less favourable than that accorded to its investors or to investors of any third state which are in a comparable situation’).

21  The importance of the variances in the formulation of FPS is still subject to debate (Malik [2011]; Mantilla Blanco [2019] 516–52). Some tribunals have argued that the differences in wording do not make a substantive difference, even in cases where the investment treaty refers only to ‘protection’ (Parkerings-Compagniet AS v Republic of Lithuania [2007] para. 354 [‘Parkerings-Compagniet’]). Other arbitral tribunals have ruled in relation to a standard requiring ‘full security and protection’ that the protection covers ‘security and legal protection’ (eg CME v Czech Republic [2001] para. 613). Similarly, formulations which explicitly make mention of ‘physical’ or ‘legal’ protection and/or security have impacted the interpretation of the standard by arbitral tribunals. This will be further discussed in Section G below.

E.  Relation with Other Standards of Treatment

22  FPS is connected to the IMS and the FET standard, and also to the customary norms on the protection of aliens. That the FPS originates in the customary international law relating to the treatment of aliens is well established (El Paso Energy International Company v Argentine Republic [2011] para. 522 [‘El Paso v Argentina’]). However, the exact relation between FPS, the IMS, and FET is still subject to much discussion and results in conceptual ambiguity on the precise position of FPS in relation to other standards of treatment as well as customary international law.

23  It has first been contended that FPS forms part of the customary international law IMS, or that both FPS and FET are included in the IMS. This approach has been adopted in the US Model BIT (2012) (in Art. 5) and by the North American Free Trade Agreement (‘NAFTA’) Free Trade Commission (‘FTC’) (NAFTA FTC [2001]; North American Free Trade Agreement [1992]). The NAFTA included a provision requiring the States to accord to investments ‘treatment in accordance with international law, including fair and equitable treatment and full protection and security’ (NAFTA Art. 1105 (1)). The NAFTA FTC interpreted this provision as not requiring ‘treatment in addition to or beyond that which is required by the customary international law minimum standard of treatment of aliens’ (NAFTA FTC [2001]). Recent multilateral treaties such as the CPTPP and the USMCA have also adopted wording specifically linking FPS and FET to customary international law and the minimum standard of treatment. The CPTPP and USMCA not only both mention FPS and FET in a provision entitled ‘Minimum Standard of Treatment’ but also make clear that FPS ‘prescribes the customary international law minimum standard of treatment of aliens as the standard of treatment to be afforded to covered investments’ and that the concepts of FPS and FET ‘do not require treatment in addition to or beyond that which is required by that standard, and do not create additional substantive rights’ (Art. 14.6. (2) USMCA; Art. 9.6. (2) CPTPP).

24  In such cases, FPS is thus considered to be part of the IMS and treatment required by the FPS clause does not exceed the protection required by customary international law (see also Noble Ventures Inc v Romania [2005] para. 164).

25  In other treaties, the link made between FPS and international law would imply that FPS requires treatment at least in accordance with the customary norm (eg US–Kazakhstan BIT [1992] Art. II (2) (a) ‘Investment … shall enjoy full protection and security and shall in no case be accorded treatment less than that required by international law’). This would leave room for a consideration that FPS requires treatment that can exceed the treatment required by customary international law. An identical clause thus was considered by an arbitral tribunal to permit the interpretation of ‘full protection and security as higher standards than required by international law’ (Azurix Corp v Argentine Republic [2006] para. 361 [‘Azurix v Argentina’]). These types of clauses thus suggest that international law then functions as a ‘floor’, compared to the situation in the previous paragraphs where international law functions as a ‘ceiling’ (Azurix v Argentina [2006] para. 361; Reinisch and Schreuer [2020] 546 ff). A similar view was expressed by the arbitral tribunal in Sun Reserve Luxco Holdings SRL v Italy (2020) (‘Sun Reserve v Italy’), in relation to ‘the most constant protection and security’ provision in the 1994 Energy Charter Treaty (Art. 10). The same article mentions after setting out the FET and FPS clause that ‘[i]n no case shall such Investments be accorded treatment less favourable than that required by international law, including treaty obligations’. The Tribunal considered that the addition of that phrase implies that the customary international law minimum standard ‘is nothing more than the absolute bare minimum standard of treatment required under international law’ and that, citing the decision in Azurix v Argentina, ‘this minimum standard constitutes a “floor, [but] not a ceiling”, of the standard of treatment that may be required from host States under the ECT’ (Sun Reserve v Italy para. 673).

26  In relation to the connection between FPS and FET, some treaties seem to suggest that FPS is part of FET. Article 3 (2) Netherlands–Nigeria BIT (1992), for instance, after requiring States to ‘ensure fair and equitable treatment of the investments’, mentions in the second paragraph that ‘[m]ore particularly, each Contracting Party shall accord to such investments full physical security and protection […]’ (emphasis added). In relation to a provision which requires States to offer ‘full protection and security in application of the principle of fair and equitable treatment’ (Art. 5 (1) Argentina–France BIT [1991] [‘protection et d’une sécurité pleines et entières, en application du principe de traitement juste et équitable’]), the Tribunal in Suez, Sociedad General de Aguas de Barcelona SA and InterAgua Servicios Integrales del Agua SA v Argentine Republic (2010) argued that FPS is thus included in FET, but that FPS is ‘narrower’ than FET (para. 165).

27  Other arbitral tribunals have contended on the contrary that FPS, FET, and the IMS, even if there is some overlap, are independent treaty standards, especially when these ‘are placed in two different provisions of the BIT’ (Jan de Nul NV and Dredging International NV v Arab Republic of Egypt [2008] para. 269). The Tribunal in Crystallex International Corporation v Bolivarian Republic of Venezuela (2016) (‘Crystallex v Venezuela’) also argued that ‘“full protection and security” is a distinct treaty standard whose content is not to be equated to the minimum standard of treatment’ (para. 632). An interpretation which would extend the scope of application of FPS to cover also legal protection and security ‘would result in an overlap with other treaty standards, notably FET, which in the Tribunal’s mind would not comport with the “effet utile” principle of interpretation’ (para. 634).

28  The overlap in and conceptual ambiguity surrounding the linkage between the FPS, FET, and IMS standards is mostly a consequence of the fact that FPS is rooted in the general rule relating to the obligation of States represented in the classical theory on the protection of aliens (El Paso v Argentina para. 522; Kläger [2011] 292). As the FET standard is also rooted in the customary international law on the minimum standard of treatment of aliens (Angelet [2022] para. 15), the conceptual distinction between FET and FPS in their contemporary emanations may indeed be open to various interpretations, even more so when FPS is interpreted as also covering legal protection and security (Lim Ho and Paparinskis [2021] 334–35).

29  At the same time, some authors have argued that while both standards are conceptually distinct, the distinction has little to no practical relevance since the finding that an act is in breach of the FET, FPS, or both standards at the same time does not ‘affect the scope of investors’ protection under the BIT’ (Angelet [2022] para. 60).

30  A final question relates to the relation between FPS and other norms regularly found in investment treaties such as ‘compensation for losses clauses’ or ‘(extended) war clauses’ (see generally Dolzer Kriebaum and Schreuer [2022] 305–9). ‘Compensation for losses clauses’ typically provide for nondiscriminatory treatment (national treatment and most-favoured-nation treatment) of foreign investors which have suffered losses to their investments in case of armed conflict, insurrection, civil disturbances, or similar events, in relation to measures of the host State in relation to such losses, such as restitution, indemnification, or compensation (see eg Art. 7 Netherlands–Nigeria BIT [1992]).

31  ‘Extended war clauses’ in turn contain provisions similar to the previously mentioned ‘compensation for losses clauses’, but in addition provide for an obligation for host States to offer restitution and/or compensation for losses suffered during armed conflict, civil strife, or related events in case of requisitioning of a covered investment by the forces or authorities of the host State, or in case of destruction of a covered investment by the forces or authorities of the host State which was not required by ‘the necessity of the situation’ (eg Art. 14.7 USMCA). Certain treaties add that the compensation should be similar to the compensation provided in case of expropriation (Art. 5 Austria–Libya BIT [2002]; Expropriation and Nationalization). An important aspect of the application of such a clause is that the acts complained of should be an act of the State, not of any other third party such as rebels or insurgents.

32  Tribunals have generally confirmed that such provisions do not as such displace the obligations of States under FPS. The Tribunal in Strabag SE v Libya (2020), for example, considered that the extended war clause contained in Art. 5 of the applicable Treaty did ‘not preclude the possibility of claims based on other provisions of the treaty with respect to the matters that also fall under Article 5 of the Treaty’ (para. 228).

F.  Types of State Conduct Covered by the FPS Standard of Treatment

33  The obligation to provide FPS applies both to (1) acts of the State and (2) acts and omissions of the State in relation to acts of private parties under the State’s jurisdiction.

G.  Scope of Application ratione materiae and Extension to Legal Protection and Security

53  The understanding that FPS applies to the acts of the State and of third parties other than State organs which threaten or impair the physical safety of the foreign investor or the investment is well accepted (see Section G.1 below). A question that has been debated for many years, however, is whether the FPS standard applies not only to physical protection and security but also extends to legal protection and security (see Section G.2).

H.  The Standard of Liability and the Influence of the Economic and Political Situation of the Host State

61  The State’s failure to meet its obligations under the FPS standard is assessed through the due diligence standard. The host State thus holds no strict liability for such harm (Salacuse [2021] 278 and 288; Lauder v Czech Republic para. 308). Earlier cases in relation to the protection of aliens had already established that such a responsibility is not an ‘indirect responsibility’ of the State for the act committed; the act which has caused harm in itself cannot be attributed to the State (British Claims in Morocco [UK v Spain] 642).

62  The concrete application of the due diligence standard, and what is then in practical terms required from States, has been the subject of several decisions. A host State should take all measures that it could reasonably be expected to take in order to prevent the occurrence of damages to the foreign investor and its investment (Salacuse [2021] 288).

63  Tribunals have often referred to the requirement that States use all ‘reasonable measures’ in preventing physical harm caused by third parties. The Tribunal in AAPL v Sri Lanka, endorsing the position of Alwyn V Freeman in his 1957 Hague Academy lecture, interpreted the FPS standard as requiring the State to take ‘reasonable measures of prevention’ (para. 77). The Tribunal in Saluka v Czech Republic argued that ‘the standard obliges the host State to adopt all reasonable measures to protect assets and property from threats or attacks which may target particularly foreigners or certain groups of foreigners’ (para. 484). In Peter A Allard v The Government of Barbados (2016) (‘Peter A Allard v Barbados’), the Tribunal interpreted FPS as requiring ‘due diligence’ or ‘reasonable care’ (para. 243; see also Cengiz v Libya para. 406), and in El Paso v Argentina the Tribunal argued that the FPS requires the State to ‘take reasonable actions within its power to avoid injury when it is, or should be, aware that there is a risk of injury’ (para. 523). Other tribunals have referred to a duty of ‘vigilance’ (AM&T v Zaire para. 6.05).

64  In practice, there seems to be little difference between the use of ‘due diligence’, ‘reasonable care’, or ‘duty of vigilance’. However, the degree of diligence or reasonableness required has been the subject of debate (see generally Mantilla Blanco [2019] 421–87). In essence, the question is whether FPS requires a certain conduct of the State which is objective or subjective, that is whether what one can expect from a State is defined in abstracto by reference to what a well-administered government could be expected to do or whether the expectations from the State depend also on the relative means available to the host State, as well as the specific circumstances present in the host State.

65  Certain authors have argued that international law adheres, generally, to the diligens paterfamilias standard (Freeman [1955] 277–78), which requires ‘nothing more nor less than the reasonable measures of prevention which a well-administered government could be expected to exercise under similar circumstances’ (ibid). This is an ‘objective’ assessment criterion. Certain decisions also suggest an objective standard (AAPL v Sri Lanka para. 77).

66  Other scholars and arbitral tribunals have instead relied on a subjective due diligence standard, taking into consideration the means that are at the disposal of the host State as well as the specific circumstances present in the host State (diligentia quam in suis) (see Pisillo-Mazzeschi [1992] 41; Brownlie [2008] 526). Aside from the practice of the IUSCT mentioned above, certain decisions of arbitral tribunals suggest that the applicable standard is a subjective due diligence standard requiring measures ‘as reasonable under the circumstances’ (Lauder v Czech Republic para. 308; see also CME v Czech Republic para. 353; El Paso v Argentina para. 523; Peter A Allard v Barbados para. 242). In Cengiz v Libya, the Tribunal considered that FPS requires

Other tribunals have advocated for the application of ‘an element of proportionality’ (Pantechniki SA Contractors & Engineers [Greece] v Republic of Albania [2009] para. 77; Proportionality).

67  Finally, it should be recalled that the obligation of States to possess and make available a judicial and administrative system is not assessed by the application of a due diligence standard. This is understandable, since the obligation is one that relates to the acts of the State itself.

I.  Conclusions

68  In the past decades, FPS has mostly become relevant as a standard for the treatment of foreign investors and their investments. It has become a standard feature of international investment agreements.

69  While formulations of FPS in these agreements vary, arbitral tribunals have often not considered the differences in wording as having any substantive impact on the protection required by host States. FPS, in the context of international investment law, requires the host State to offer foreign investors and their investment protection from physical injury and damage, caused either by the State or by private parties. It covers both a duty from the State to prevent physical injuries and a duty to apprehend those responsible for the act. It also contains an obligation by the State to make available to aliens a functioning judicial and administrative system.

70  Despite its ancient roots, the precise scope of application of FPS is also subject to debate in the practice of arbitral tribunals. In addition to the connection between FPS, the IMS, and FET, a question that has not yet been settled is the extension of the scope of application of FPS to legal protection and security. Such an interpretation of FPS brings the scope of application of the standard close to FET, although certain tribunals have explained that the two standards are autonomous and different in their scope of application. In general, however, it is accepted that the current conception of the FPS standard of treatment, however phrased, comprises protection from physical injuries and harm.

71  It is also well established that FPS, in relation to acts of private parties, requires an assessment of the State’s duty of prevention and repression by reference to a due diligence standard. A State has no strict liability for the harm caused by the acts of third parties, in that harm caused by private parties can result in State responsibility only if the State has not acted in due diligence to prevent such acts of third parties. The application of FPS in relation to acts of the State or State organs, in turn, is not assessed through the standard of due diligence. A State can then be held responsible for acts that infringe the protection and security of aliens if such acts are attributable to the State (as in the case of physical harm caused to an investment in case of civil strife or unrest by the State’s own military or police force). The question of whether the due diligence standard allows for the taking into consideration of the specific economic and political situation of the State allegedly responsible for the breach of the standard is also subject to debate. Despite the agreement that due diligence applies to acts of private parties, arbitral tribunals have not unequivocally accepted that due diligence allows an assessment based on the relative capacities of and the specific circumstances applicable within the host State.