Iran’s Threat of Retaliation

[Sava Janković is an Assistant Professor of International Law and Visiting Scholar at Durham Law School.]

[Volker Roeben is a Full Professor of International Law and Dean of Durham Law School.]

[Francis Grimal is a Reader in Public International Law at the University of Buckingham and Co-Editor-in-Chief of the Journal on the Use of Force and International Law.]

Introduction

Towards the end of August 2024, Iran vowed retaliation after the prominent Hamas leader, Ismail Haniyeh, was killed in Tehran following his attendance at the inauguration of Iran’s president, Masoud Pezeshkian, sparking concerns in Israel about the possibility of an imminent attack. This situation further coincided with the killing of Fuad Shukr, a senior Hezbollah commander (also supported by Iran), in an Israeli airstrike on a suburb of Beirut, the Lebanese capital.

Time has since passed without any major response to those initial threats by the international community leaving Israel and the broader Middle East in a state of on-going hostility and tension. While the nature and severity of Iran’s overall response remains unclear, Iran has issued a prime facie threat directed at Israel to use force. This threat is being taken seriously, with several Western leaders contacting Iran’s leadership, urging restraint. However, the spokesperson for Iran’s Ministry of Foreign Affairs dismissed these pleas as lacking in ‘political logic and contradicting principles of international law’.

This is certainly a highly sensitive and political matter. But it also raises important questions of the applicable international legal framework vis threats of force (as opposed to their actual use), which Art. 2(4) of the UN Charter prohibits. Similarly, it highlights the lack of guidance that international law is able to provide states when dealing with such threats. It is with these questions that the following comments are concerned, first discussing the credibility of the threat of force, and secondly, exploring possible grounds for legal justification.

Credibility of the Threat of Force

The credibility of threats of force plays a major role in assessing threats from both a strategic and  the legal perspective. Arguably, non-credible threats, whether voiced or not, attract minimal legal consequences, with some scholars even suggesting they fall outside the scope of international law (Lagerwall & Dubuisson, p. 915; Hofmeister, p. 111). Conversely, credible threats are easier to establish, making it simpler to determine their prima facie illegality and to calibrate an appropriate response, including holding the wrongdoer accountable.

The substantial Russian military buildup near Ukraine’s borders preceding the full-scale invasion in February 2022 was neither officially declared nor intended as an overt threat to Ukraine; in fact, Russian officials outright denied any plans for future military action. Some states in the UN Security Council, such as China, India, Ghana, and Belarus, viewed it either a sovereign prerogative or not as a threatening behavior. This type of implicit threat creates a blind spot in international peace and security law. However, it should be assessed by the standard set in the IIFFMCG’s report, which provides valuable insights into targeting behaviour, indicating that militarised acts become threatening

‘as soon as they are non-routine, suspiciously timed, scaled up, intensified, geographically proximate, staged in the exact mode of a potential military clash, and easily attributable to a foreign policy message, the hostile intent is considered present and the demonstration of force manifest’ (at 232).

The credibility of verbal threats, such as Iran’s now, should be weighed against factors such as the military capacity of the threatening party, its history of involvement in military actions, the overall geopolitical situation, and the reactions of other states. In other words, the cumulative  holistic context.

The current crisis coincides with a particularly sensitive period for Iran. Analysts suggest that the country is grappling with how to respond in a way that punishes the assassination on its soil without triggering a full-scale war with a formidable opponent. In addition, divergent goals and priorities between Iran and Hezbollah, along with the desire to avoid another failure in penetrating Israeli air defenses, could influence both the decision and timing of any retaliation. This situation is further complicated by the recent installation of a new government in Tehran, which may be contributing to the delay in deciding how to respond. Statements like those from last week from Iran’s acting foreign minister that the country would respond to the killing of Haniyeh at the “right time” in the “appropriate” manner, reduce the likelihood of immediate retaliation. Furthermore, the US response, involving the deployment of additional fighter squadrons and more warships to the Middle East to help defend Israel, may diminish the chances of Iranian reprisals.   

On the other hand, Iran certainly has the capacity to retaliate militarily, as evidenced in April when it launched more than 300 missiles and drones at Israel. The decision of certain airlines to halt operations to the Middle East and the calls by states for their citizens to evacuate from Lebanon, suggests an increased likelihood of military action, thereby heightening the overall threat.

Threats in Self-Defense

As the International Court of Justice (ICJ) prominently established in the Nuclear Weapons Advisory Opinion, ‘if the use of force itself in a given case is illegal […] the threat to use such force will likewise be illegal’. On the other hand, ‘if it [the threat] is to be lawful, the declared readiness of a State to use force must be a use of force that is in conformity with the Charter’ (para. 47).

Therefore, for Iran to lawfully justify its threats, it must do so within the framework of Article 51 of the UN Charter, bearing in mind that any use of force must be necessary and proportionate, noting of course the reporting requirement under Article 51 to the UN Security Council. Yet, it remains doubtful whether these requirements apply to threats of force in self-defence, especially considering the lack of authoritative opinion on this issue, both in practice and scholarship. Arguably, Iran’s threat could also be justified within the context of an ongoing, albeit small conflict, which might escape the legal requirements valid during peacetime and the necessity to respond ‘quickly’ to an armed attack. However, the use of force, and by extension threats issued in response to a bygone or current non-imminent threat of an armed attack, have weak legal underpinnings.

If we accept that the conflict between Iran and Israel has not escalated to the level of an international armed conflict (IAC), despite their mutual nonrecognition, then the killings of prominent Islamic figures in Tehran and Beirut may not be sufficient to trigger a response under Article 51 of the UN Charter. There does remain debate as to whether a breach of Article 2(4) in of itself triggers legitimacy of response or whether it is the sine qua non requirement of an armed attack (amounting to a grave use of force) under the tapestry of Article 51 of the UN Charter and applicable customary law. Additionally, these incidents do not easily fit within the scope of acts of aggression as defined in Article 3 of UNGA Res 3314. While the assassination of Haniyeh in Tehran, likely involving the planting of a bomb, might suggest the “sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries,” the act appears to fall short of the substantial gravity required by the remaining part of the paragraph to constitute an armed attack.

This raises the question: what should the required threshold be, and what is the kind of severity armed force is necessary to justify self-defense?

The assassination of the Hamas leader in Tehran constitutes a violation of Iran’s sovereignty and territorial integrity—a breach of Article 2(4). This language is commonly used by leaders when addressing extrajudicial targeted killings. For example, former US Secretary of State Mike Pompeo expressed the view that ‘[t]he killing, the murder of Jamal Khashoggi in the consulate in Turkey violates the norms of international law. That much is very, very clear.’ Similarly, in 2018, the UK, US, Germany and France in a joint statement regarding the poisoning of Sergei and Yulia Skripal in the British town of Salisbury remarked ‘It is an assault on UK sovereignty and any such use by a State party is a clear violation of the Chemical Weapons Convention and a breach of international law.’ Unfortunately, as Jovanovic notes, not much attention is paid to the human right to life, or at best, it is not clearly articulated.

However, the situation is quite distinct here, as it involves the assassination of a leader from a political and military organization that wields power in Gaza, who also served as prime minister of the Palestinian National Authority. If we accept that under international law Palestine has the right to resist militarily based on its right to self-determination—both in its quest for statehood and in opposing Israeli military occupation, as recently confirmed by the ICJ’s Advisory Opinion on the Policies and Practices of Israel in the OPT – then Hamas leaders might be considered to enjoy elevated rights under international law, possibly even an informal right to immunity.

Although the Palestine Liberation Organization (PLO) is internationally recognized as the representative of the Palestinian people, it is Hamas that actually conducts trials ‘on the ground’ to reestablish political control in accordance with the right to self-determination and UNGA Resolution 37/43. This resolution reaffirms ‘the legitimacy of the struggle of peoples for independence, territorial integrity, national unity and liberation from colonial and foreign domination and foreign occupation by all available means, including armed struggle’. It this context Turkish President Erdogan invoked international law condemning the assassination of Haniyeh as ‘a despicable attempt to undermine the Palestinian cause, the glorious resistance of Gaza, and the rightful struggle of our Palestinian brothers, aiming to demoralize, intimidate, and suppress them’.

The Organization of Islamic Cooperation (OIC) issued a statement denouncing the assassination as ‘a crime of aggression, a flagrant violation of international law and the UN Charter and a serious infringement of the sovereignty, territorial integrity and national security of the Islamic Republic of Iran’.

However, the assassination was not qualitatively grave enough to constitute an armed attack that would justify recourse to self-defense under Article 51 of the UN Charter.  

A Grey Area?

Even if Iran is not authorized to threaten force under international law, current international efforts focus primarily on preventing the effects of such threats, rather than on addressing the threats themselves or sanctioning them. There may be an implicit understanding that deviates from the stricter conclusions of the Nuclear Weapons Advisory Opinion. Specifically, the threat of force in response to the extrajudicial and extraterritorial killing of a high-ranking individual within domestic settings (even if they are considered leaders of terrorist organizations, such as Hamas, which is designated as a terrorist organization by the US and the EU) might be viewed as a proportionate response as long as it does not materialize into actual use of force. In such cases, the (un) lawfulness of threats might not be subject to the retroactive scrutiny of the lawfulness of the use of force. This is, at best, currently a grey area of the law of international security. Yet, maintaining legal certainty, which is essential in this area, militates against entertaining or solidifying it. The system that has been set out here provides states with clearer guidance, conducive to the maintenance of international security.

Conclusions

Threats of force are prohibited under Article 2(4) of the UN Charter, just as the use of force is. The current situation in the Middle East underscores the practical importance of this prohibition. Yet the law remains underdeveloped conceptually and in practice. It is highly desirable to clarify this area to offer states more precise legal guidance. These comments have sought to demonstrate that a rigorous analysis of threats under the UN Charter law can provide such guidance.