134 Report of the International Law Commission on the work of its fifty-third session all circumstances, including armed conflict.775 The same applies, mutatis mutandis, to consular officials. (15) In the United States Diplomatic and Consular Staff in Tehran case, ICJ stressed that “diplomatic law itself provides the necessary means of defence against, and sanction for, illicit activities by members of diplomatic or consular missions”,776 and it concluded that violations of diplomatic or consular immunities could not be justified even as countermeasures in response to an internationally wrongful act by the sending State. As the Court said: The rules of diplomatic law, in short, constitute a self-contained regime which, on the one hand, lays down the receiving State’s obligations regarding the facilities, privileges and immunities to be accorded to diplomatic missions and, on the other, foresees their possible abuse by members of the mission and specifies the means at the disposal of the receiving State to counter any such abuse.777 If diplomatic or consular personnel could be targeted by way of countermeasures, they would in effect constitute resident hostages against perceived wrongs of the sending State, undermining the institution of diplomatic and consular relations. The exclusion of any countermeasures infringing diplomatic and consular inviolability is thus justified on functional grounds. It does not affect the various avenues for redress available to the receiving State under the terms of the Vienna Convention on Diplomatic Relations and the Vienna Convention on Consular Relations.778 On the other hand, no reference need be made in article 50, paragraph 2 (b), to multilateral diplomacy. The representatives of States to international organizations are covered by the reference to diplomatic agents. As for officials of international organizations themselves, no retaliatory step taken by a host State to their detriment could qualify as a countermeasure since it would involve noncompliance not with an obligation owed to the responsible State but with an obligation owed to a third party, i.e. the international organization concerned. Article 51. Proportionality Countermeasures must be commensurate with the injury suffered, taking into account the gravity of the internationally wrongful act and the rights in question. Commentary (1) Article 51 establishes an essential limit on the taking of countermeasures by an injured State in any given case, based on considerations of proportionality. It is relevant in determining what countermeasures may be applied and 775 See, e.g., Vienna Convention on Diplomatic Relations, arts. 22, 24, 29, 44 and 45. 776 United States Diplomatic and Consular Staff in Tehran (see footnote 59 above), p. 38, para. 83. 777 Ibid., p. 40, para. 86. Cf. article 45, subparagraph (a), of the Vienna Convention on Diplomatic Relations; article 27, paragraph 1 (a), of the Vienna Convention on Consular Relations (premises, property and archives to be protected “even in case of armed conflict”). 778 See articles 9, 11, 26, 36, paragraph 2, 43 (b) and 47, paragraph 2 (a), of the Vienna Convention on Diplomatic Relations; and articles 10, paragraph 2, 12, 23, 25 (b) and (c) and article 35, paragraph (3), of the Vienna Convention on Consular Relations. their degree of intensity. Proportionality provides a measure of assurance inasmuch as disproportionate countermeasures could give rise to responsibility on the part of the State taking such measures. (2) Proportionality is a well-established requirement for taking countermeasures, being widely recognized in State practice, doctrine and jurisprudence. According to the award in the “Naulilaa” case: even if one were to admit that the law of nations does not require that the reprisal should be approximately in keeping with the offence, one should certainly consider as excessive and therefore unlawful reprisals out of all proportion to the act motivating them.779 (3) In the Air Service Agreement arbitration,780 the issue of proportionality was examined in some detail. In that case there was no exact equivalence between France’s refusal to allow a change of gauge in London on flights from the west coast of the United States and the United States’ countermeasure which suspended Air France flights to Los Angeles altogether. The tribunal nonetheless held the United States measures to be in conformity with the principle of proportionality because they “do not appear to be clearly disproportionate when compared to those taken by France”. In particular, the majority said: It is generally agreed that all counter-measures must, in the first instance, have some degree of equivalence with the alleged breach: this is a well-known rule … It has been observed, generally, that judging the “proportionality” of counter-measures is not an easy task and can at best be accomplished by approximation. In the Tribunal’s view, it is essential, in a dispute between States, to take into account not only the injuries suffered by the companies concerned but also the importance of the questions of principle arising from the alleged breach. The Tribunal thinks that it will not suffice, in the present case, to compare the losses suffered by Pan Am on account of the suspension of the projected services with the losses which the French companies would have suffered as a result of the counter-measures; it will also be necessary to take into account the importance of the positions of principle which were taken when the French authorities prohibited changes of gauge in third countries. If the importance of the issue is viewed within the framework of the general air transport policy adopted by the United States Government and implemented by the conclusion of a large number of international agreements with countries other than France, the measures taken by the United States do not appear to be clearly disproportionate when compared to those taken by France. Neither Party has provided the Tribunal with evidence that would be sufficient to affirm or reject the existence of proportionality in these terms, and the Tribunal must be satisfied with a very approximative appreciation. 781 In that case the countermeasures taken were in the same field as the initial measures and concerned the same routes, even if they were rather more severe in terms of their economic effect on the French carriers than the initial French action. (4) The question of proportionality was again central to the appreciation of the legality of possible countermeasures taken by Czechoslovakia in the GabčíkovoNagymaros Project case.782 ICJ, having accepted that 779 “Naulilaa” (see footnote 337 above), p. 1028. Air Service Agreement (see footnote 28 above), para. 83. 781 Ibid.; Reuter, dissenting, accepted the tribunal’s legal analysis of proportionality but suggested that there were “serious doubts on the proportionality of the counter-measures taken by the United States, which the tribunal has been unable to assess definitely” (p. 448). 780 782 Gabčíkovo-Nagymaros Project (see footnote 27 above), p. 56, paras. 85 and 87, citing Territorial Jurisdiction of the International Commission of the River Oder, Judgment No. 16, 1929, P.C.I.J., Series A, No. 23, p. 27.