By Niloufar Omidi, PhD in International Human Rights Law from Irish Centre for Human Rights, NUI Galway with focus on the right to peace, and the implementation mechanisms of this right through international legal instruments
The present blog post examines the extent to which threats by Iran or the United States can trigger the right of self-defence for the other side in view of jus contra bellum, considering the escalation of tensions between the two states since May 2019 when US sanctions on Iran were reinstated, and subsequently, exemptions from sanctions for countries still buying oil from Iran were terminated. To this purpose, it examines the approaches of the two conflicting states to the law of self-defence, on the one hand, and the law of self-defence in the context of jus contra bellum, on the other hand.
Following the 11 September 2001 terrorist attack, the US invaded Afghanistan, to exercise the right of self-defence, and to prevent and deter further attacks on the US, considering Security Council resolutions 1368 (2001) and 1373 (2001). Subsequently, in 2003, the US carried out a military intervention in Iraq, claiming to be acting for eliminating the imminent threat of Saddam Hussein’s weapons of mass destruction and defeating terrorism. These two armed conflicts carried out by the US were claimed as self-defence against indirect aggression and pre-emptive self-defence respectively. In order to explore Iran’s understanding of self-defence, the Iran-Iraq War (1980-1988) can be considered. This war was prolonged for eight years due to the insistence of the aggressed state, namely Iran, on continuing the war for the purpose of self-defence, while the aggressor was willing to reconcile within the second year of the war. However, as de Zayas discusses, “even in a legitimate self–defence situation, this does not justify the continuation of a war”.  According to Corten, the taking of necessary measures by the UN Security Council impairs the exercise of the inherent right of self-defence, where this right might have remained.  Additionally, the Security Council binding measures under Article 25 are superior to the right of self-defence.  As it can be observed, both sides involved in this tension, Iran and the US, have had a very broad interpretation of the right of self-defence, with backgrounds in justifying their illegal use of force as act of self-defence. In fact, as Bassiouni elaborates, in the realpolitik view of international relations “every conflict is sui generis and that the variables of each conflict are so diverse that cannot be categorized or characterized in a way that a common international legal regime can apply to all these heterogeneous conflicts”. 
Conversely, jus contra bellum is subject to an extremely restrictive interpretation under the law on the use of force and its exceptions, namely self-defence and intervention authorised by the Security Council. The International Court of Justice (ICJ) has constantly adopted a strict interpretation of the right of self-defence in its judgements in Nicaragua (para 195, 230, 247), Oil Platforms (para 51, 64)and DRC v Uganda (para 146). Furthermore, in the Wall Advisory Opinion the Court rejected the claim by Israel that “the construction of the Barrier is consistent with Article 51 of the UN Charter, its inherent right to self-defence and Security Council resolutions 1368 (2001) and 1373 (2001)” (para138, 139). The ICJ’s interpretation of self-defence is based on Article 3(g) of UNGA Resolution 3314 (XXIX) defining aggression, Article 51 of the UN Charter and the two requirements for self-defence in customary law, namely necessity and proportionality. As Gray asserts, the Court “has resisted calls to widen its view of the scope of self-defence”. 
In the restrictive approach to the scope of self-defence, gravity and intention seem crucial to be considered to determine the existence of an armed attack. As gravity can be more objectively and tangibly assessed, it is a means by which to clarify prima facie the existence of the intention. Additionally, the threat of force is illustrated as merely recognized, evidently established, and expressly formulated threats.  Corten asserts that the preventive self-defence or right to counter the threat of an armed attack, including anticipatory self-defence, is not of legal basis in international law. However, he recognises a right to self-defence to defy the use of force which has materially started but has not reached the targeted territory.  The ICJ, in DRC v Uganda, implicitly rejected pre-emptive self-defence based on its interpretation within the strict confines of Article 51 of the UN Charter. (para148) However, this argument is more difficult to sustain with regard to possible armed attacks involving the use of nuclear weapons, given the nature of these weapons which are not capable of being proportionate. 
The ICJ asserted, in Nicaragua, that “self-defence would warrant only measures which are proportional to the armed attack and necessary to respond to it”.(para176) Necessity requires neutral evaluation of whether the action is exclusively performed through the authourised mechanism of self-defence. In this assesment, three factors should be considered: immediacy of the action in self-defence after the attack; the effectiveness or adequacy or appropriatness of the self-defence measures; and the proportionality of the actionAccording to the International Law Commission’s Rapporteur on State Responsibility, Roberto Ago, “Self-defence will be valid as a circumstance precluding the wrongfulness of the conduct of the State only if that State was unable to achieve the desired result by different conduct involving either no use of armed force at all or merely its use on a lesser scale”.  It can be observed that the use of force for the purpose of even legitimate self-defence is the last option in the context of jus contra bellum, and thus, incursions into another country’s territory cannot easily be justified. (see US Diplomatic & Consular Staff in Tehran, para93)
The other dilemma regarding self-defence is its legality in response to indirect aggression, which became more controversial since the US invasion of Afghanistan (2001). Indirect aggression is defined as the involvement of a state in an armed attack against another state through non-state actors.  In this category, one should mention the explosions in the Persian Gulf caused by the Houthis, who are backed by Iran. According to the ICJ in Corfu Channel, it is “every State’s obligation not to allow knowingly its territory to be used for acts contrary to the rights of other States” (p. 22). Additionally, the arming and training of armed opposition forces, and also the supply of funds, could amount to unlawful intervention.(Nicaragua para 228) Nevertheless, as Corten argues, this kind of state involvement can be below the gravity threshold of an armed attack by states under Article 51, and thus it cannot trigger the right of self-defence.  Similarly, Ruys concludes that slight support, funding and hosting a group within the territory of a state may amount to a breach of Art 2(4), but it cannot be sufficient to trigger the right of self-defence. 
Self-defence has a delicate framework, and in certain conditions, some cases of use of force claiming self-defence could actually constitute an act of aggression. As Dinstein analyses, “[o]nly when the universal liberty to go to war was eliminated, could self-defence emerge as a right of signal importance in international law […] The evolution of the idea of self-defence in international law goes ‘hand in hand’ with the prohibition of aggression”. However, the international law system suffers from several deficiencies in the prohibition of aggression, especially in its implementation, given that several powerful states, included 3 permanent members of the Security Council, are not party to the International Criminal Court (which has jurisdiction over the crime of aggression in virtue of Art 8 bis of the Rome Statute). In order to overcome the existing deficiencies, as Franck suggests, Article 51 should be applied by a “quasi-jury” in the international system that includes the Security Council, the General Assembly, the ICC and the ICJ.  In fact, this issue is not only a political but also a legal problem.  In this way, the Security Council should be accountable, considering its legal personality when it fails to fulfil its responsibility. Article 39 of the UN Charter grants the Security Council authority to decide whether a situation is a threat to peace, a breach of peace or an act of aggression, with no accountability regarding its decisions. The political nature of this body and the veto power of its five permanent members can be problematic, especially when the breach of peace is committed by one of the so-called P-5 or its allies. To solve this problem, as Henderson discusses, this political body can at least be “answerable internally within the UN”.  In this way, the law of self-defence will not be at the mercy of political considerations.
can be observed self-defence can be problematic when it is broadly interpreted
and when it provides excuses for engaging in war. Unfortunately, Iran
and the US have already loosely interpreted the right of self-defence in
justifying their illegal use of force as act of self-defence. In recent
tensions between the two states, both Iran
US are justifying the probable use of force as
act of self-defence and defending their own national interests and security
that can lead to another war in the region. However,
Jus contra bellum adopts a
restrictive methodology concerning exceptions to the prohibition of the use of
force which is contrary to policy-oriented extensive approaches to issues such as
pre-emptive self-defence. In the context of jus
contra bellum, there is less legal basis for self-defence against indirect
aggression (e.g. Afghanistan War) and pre-emptive self-defence (e.g. Iraq War).
Therefore, such threats that have been made by
Iran and the US are breaches of Article 2(4), but they do not amount to
triggers of the right of self-defence, as not all requirements for the law of
self-defence are fulfilled. (see Sep. Op. Judge Kooijmans, Oil
Platforms, para63) In this context, these threats cannot justify any recourse
to the use of force, and thus, the right of self-defence cannot be a legal
basis for an armed attack. Nevertheless, this does not affect the responsibility of the Security
Council to consider these threats to peace and to take appropriate measures.
 Rein Müllerson, ‘Jus ad Bellum & International Terrorism‘ in Yoram Dinstein and Fania Domb (eds), ‘The Progression of International Law: Four Decades of the Israel Yearbook on Human Rights – An Anniversary Volume’ (Martinus Nijhoff Publishers, 2011), p.579; John Quigley, ‘The Afghanistan War and Self-Defense’ (2003) 37 (2) Valparaiso University Law Review, p. 542.
 Sanjay Gupta, ‘The Doctrine of Pre-Emptive Strike: Application and Implications during the Administration of President George W. Bush’ (March 2008) 29 (2) International Political Science Review, p. 181.
 Alfred De Zayas, ‘Peace as a Human Right: The Jus Cogens Prohibition of Aggression‘ in Asbjorn Eide, Jakob Th Moller and Ineta Ziemele (eds), ‘Making Peoples Heard: Essays on Human Rights in Honour of Gudmundur Alfredsson’ (Martinus Njhoff Publishers, 2011), p. 34.
 Olivier Corten, ‘The Law Against War: The Prohibition on the Use of Force in Contemporary International Law’ (Sutcliffe, C. (tr), Hart Publishing 2010), p. 474-5.
 Raphaël van Steenberghe, ‘The Law Against War or Jus Contra Bellum: A New Terminology for a Conservative View on the Use of Force? ‘ (2011) 24 Leiden Journal of International Law, p.781.
 M Cherif Bassiouni, ‘Searching for Peace and Achieving Justice: The Need for Accountability’ (Fall 1996) 59 (4) Law & Contemp Probs, p.13.
 Christine Gray, ‘The ICJ and the Use of Force‘ in Christian J. Tams and James Sloan (eds), ‘The Development of International Law by the International Court of Justice’ (OUP, 2013), p. 259.
 van Steenberghe, ‘The Law Against War or Jus Contra Bellum: A New Terminology for a Conservative View on the Use of Force? ‘ (2011), p. 759.
 Corten, ‘The Law Against War: The Prohibition on the Use of Force in Contemporary International Law’ (2010), pp. 414,416.
 Gray, ‘The ICJ and the Use of Force‘ (2013), p. 256.
 Corten, ‘The Law Against War: The Prohibition on the Use of Force in Contemporary International Law’ (2010), pp. 484-486.
 ILC, Yearbook of the International Law Commission, 1980, Vol. II, Part One, UN Doc. A/CN.4/SER.A/1980/Add.l (Part 1), p. 69.
 van Steenberghe, ‘The Law Against War or Jus Contra Bellum: A New Terminology for a Conservative View on the Use of Force? ‘ (2011), p. 779.
 Corten, ‘The Law Against War: The Prohibition on the Use of Force in Contemporary International Law’ (2010). p. 444.
 Tom Ruys, ‘Armed Attack’ and Article 51 of the UN Charter: Evolutions in Customary Law and Practice’ (CUP 2010), p. 390.
 Yoram Dinstein, ‘War, Aggression and Self-Defence’ (2nd (edn) CUP 1995), pp. 176-177.
 Thomas M Franck, ‘Recourse to Force: State Action against Threats and Armed Attacks’ (CUP 2003), p. 67.
 Niels Blokker, ‘The Crime of Aggression and the United Nations Security Council’ (December 15, 2007) 20 (4) Leiden Journal of International Law, p. 880.
 Christian Henderson, ‘Authority without Accountability? The UN Security Council’s Authorization Method and Institutional Mechanisms of Accountability’ (December 1, 2014) 19 (3) Journal of Conflict and Security Law, p. 492.