Iran and Israel have been engaged in intermittent hostilities for years. But the latest rounds of strikes – by Israel against Iran’s consulate in Damascus on April 1, killing seven Iranian government officials including multiple senior officials of Iran’s Revolutionary Guard Corp (IRGC), and by Iran launching over 300 drones and missiles towards Israeli territory in response on Saturday, April 13 – have threatened to escalate tensions into an all-out regional war. Iran’s strikes against Israel were unprecedented in scale and in being directed at Israeli territory, but have not targeted central Israel, and were indeed largely repelled by Israeli and regional defense systems. The United States, Arab countries, and the UN Secretary General are trying to de-escalate the situation and restrain the parties from further hostilities, with U.S. President Joe Biden imploring Israeli Prime Minister Benjamin Netanyahu in a leader to leader call to “slow things down.” Israel, nevertheless, has vowed to respond to Iran’s attack. 

We asked leading expert Eliav Lieblich, a Professor at Tel-Aviv University’s Faculty of Law, about the legality of recent attacks by Iran and Israel, how Israel’s domestic politics might impact its response to Iran’s April 13 attack, and prospects for de-escalation. 

Q-1. In its Article 51 letter to the Security Council, Iran stated its April 13 attacks on Israel were taken “in the exercise of Iran’s inherent right to self-defence as outlined in Article 51 of the Charter of the United Nations, and in response to the Israeli recurring military aggressions, particularly its armed attack on 1 April 2024 against Iranian diplomatic premises.” Does Iran have a valid self-defense claim for these strikes?

Answering this question reveals the exceedingly difficult task of applying jus ad bellum in the current crisis. One key reason for this is the active participation in hostilities of armed non-state actors across at least five states and territories, all having some affiliation with Iran or the IRGC. The relationship between Iran and these actors is crafted to leave space for plausible deniability regarding state responsibility for specific actions. It seems that to Israel, the entire self-described “axis of resistance” is viewed as one actor  – a web of state and non-state actors conducting ongoing hostilities and pursuing a joint strategy against it. In this sense, what Iran describes as “recurring military aggressions” by Israel, would be described by the latter as recurring acts of self-defense against this unitary web.

So whether Iran has a valid claim of self-defense requires first determining whether the conduct of the involved non-state actors is attributable to Iran, either through overall control (some would posit the higher threshold of “effective control”) or substantial involvement in their actions. This is on top of the even more complex question of jus ad bellum in the relations between Israel, Lebanon, and Syria, which is complicated because of border disputes, the occupation of the Golan Heights, existing UNSC resolutions, and other factors. 

Setting these complexities aside, specifically regarding the Iranian attack on Israel on April 13, the main problem with Iran’s Article 51 argument here is that its response took place two weeks after the attack to which it was allegedly responding, and was repeatedly phrased by Iran’s leaders as an act of punishment or retaliation. This makes it a prohibited forcible reprisal rather than a defensive action. 

The same logic would also apply to Israel if it decides to resort to force as a response to Iran’s April 13 attack in the coming days. Israel might argue, in this context, that it does not need to provide a separate jus ad bellum justification for such a response since it would be part of an ongoing conflict with Iran and its proxies. I don’t find this type of argument convincing since, in my view, jus ad bellum must apply throughout an armed conflict, along with International Humanitarian Law (IHL), if it is to have any meaning.                

Q-2. There appears to be an increasing cadence of attacks publicly stated to be retaliatory, or punishment for prior hostile acts by militias or state actors, even though these are not lawful bases for the use of force, as many international lawyers have noted. U.S. strikes against so-called “Iran-backed militias” have often been described this way, as have a number of the attacks in the Iran-Israel context. But the story may not end with statements made from the podium about retaliation. U.S. “Article 51 letters” to the UN Security Council justifying its strikes against Iran-backed militias, for example, describe the attacks as necessary and proportionate measures aimed at preventing further attacks against its own forces on the part of these militias. 

There are a range of views on whether it is lawful for a State to use force in self-defense when an armed attack against it has already been completed – that is, there is no attack underway or imminent at the time of the response – but when there has been an ongoing series of attacks, and there is some reasonable expectation that they might continue. Some argue that accepting a right of self-defense in such scenarios is too permissive, and goes beyond what the UN Charter or customary international law allow. Others argue that any other approach is under-protective of States’ inherent right to defend themselves from armed attacks. 

Do you think the weight of opinion in the international legal community now views the use of force in self-defense in such situations to be lawful? Does that view strike the right balance?

First, many states recently have been employing language that is closer to prohibited reprisals than legitimate self-defense – the United States and its allies in strikes against Iranian-backed regional militias; Iran in its strikes in Iraq, Pakistan, and Israel; and Israel in its threat to respond to Iran’s April 13 attack.  Sometimes, these states speak differently on the “political” and “legal” levels, and when submitting their Article 51 letters they try to squeeze their actions into some remotely plausible self-defense argument. In my view these “political” statements undermine the credibility of the legal argument later on. Overall, the terrifying turn of events in the recent week exemplifies the wisdom in international law’s prohibition on forcible reprisals, and also the fact that any actor that invokes an exceedingly permissive interpretation of jus ad bellum will have to come to terms that its adversaries will also utilize it.   

Nonetheless, in my view and the view of others, there is a good case to be made that a series of attacks, combined with a clear intention to continue them or an imminent threat to do so, gives rise to a right of self-defense against the specific threat even after an attack was purportedly “completed.” If we accept that preemptive self-defense against an imminent attack might be lawful even before an attack takes place (as per the Caroline doctrine), the same logic applies a fortiori after a pattern of attacks – which essentially serves as strong evidence for the imminent threat of further attacks. Of course, assessing such scenarios in real life becomes difficult when we have a long exchange of response and counter-response such as between Israel and Lebanese Hezbollah –  where it is difficult to pinpoint where the duty of disengagement lies (i.e., the point in which if one party ceases to respond it is clear that the other would cease attacking). 

But we really need to differentiate such cases from situations in which a state retaliates against an isolated attack after it is completed, and when there are no serious prospects for further imminent attacks. Here, states often use the term “deterrence” loosely to portray an essentially punitive act as a defensive one. The trouble with deterrence-based justifications is not only their speculative nature, but also that they can always be utilized to mask an act of retribution as a forward-looking act of prevention. This is precisely why relying on deterrence as justification is so dangerous for any attempt to legally regulate the resort to force.          

Q-3. Switching gears, the UN Secretary General has called for de-escalation, stating in an emergency session on Sunday that now “is the time to defuse and de-escalate” and to exercise “maximum restraint.” This seems to echo the views of the United States, which is widely seen as protecting Israel in the Security Council, but which has itself relied on a legal theory of self-defense that looks similar to Iran’s case for its most recent strikes against Israel. Will it be paralysis-as-usual, or is there a role for the Security Council here?

I think we need to broaden the analysis here. Yes, the United States usually uses its veto power to “protect” Israel, but we have here a complex array of interests, and particularly the emerging strategic alliance between Russia and Iran. It is clear that a meaningful engagement by the U.N. Security Council also would need to provide solutions to the situation in Lebanon that Iran would not favor, and whether a meaningful engagement by the Security Council would be prevented has to do not only with the United States but also with how the other permanent members of the Council – China, France, Russia, and the United Kingdom – will act. 

Q-4: Can Israel make a plausible legal case that there is a reasonable expectation that attacks from Iran might continue, and that it is therefore necessary to act in self-defense, despite official Iranian statements that the attack has “concluded”? 

I think Israel would be hard-pressed to make such an argument precisely because Iran’s direct attack on Israeli territory was unprecedented, so it would be difficult at this point to argue that there is a pattern of attacks that reasonably establishes that further attacks of this type are incoming from Iran. But again, whether Iran’s operations have indeed been “concluded” reverts to the question of how we understand the involvement of Iran in ongoing operations by non-state actors in the region. Consider, for example, the statement by the U.S. delegation at Sunday’s emergency meeting of the U.N. Security Council. “The United States also supports Israel’s exercise of its inherent right to defend itself in the face of this attack …And let me be clear – if Iran or its proxies take actions against the United States or further action against Israel, Iran will be held responsible.” 

I would argue that in any case, even if we view Iran as an active participant in these hostilities, strikes on Iranian territory probably would be disproportionate on the ad bellum level at this point.

Q-5. Commentators have suggested that Israeli Prime Minister Benjamin Netanyahu’s domestic political troubles are playing a role in his willingness to widen the conflict that has been worsening since Hamas’ Oct. 7 attack against Israel, rather than trying to contain it. Do you think domestic politics will factor into Israel’s decision as to whether – and how – it responds to Iran in the coming days or weeks? 

Unfortunately, the overriding consideration in Netanyahu’s decision making in recent months is apparently the need to preserve his coalition, which means continuously catering to far right ministers, even at the expense of Israel’s most important strategic alliances. These ministers have been very vocal about the need to respond forcibly against Iran, and Netanyahu is absolutely dependent on them for political survival. It is true that the government authorized the more moderate war cabinet – which also includes centrist ministers who are Netanyahu’s political rivals – to decide what to do in this case, but Netanyahu is unlikely to completely disregard his hardcore electoral base. It’s unclear what he will eventually do, but domestic politics will certainly play a central role.     

Q-6. As a matter of jus in bello (eg the Geneva Conventions), are Iran and Israel already in an “armed conflict” and, if so, what would be the legal implications of this? 

Again, answering this requires making a determination regarding the legal relations between Iran and the various actors with which Israel is engaged in ongoing hostilities. If we think that the actions of these groups are attributable to Iran, then there is definitely an international armed conflict between Iran and Israel. If they are not attributable to Iran, the question is whether the sporadic exchanges between Israel and the IRGC, mainly in Syria, create an ongoing armed conflict between them. The accepted standard is that once an international armed conflict begins – when a state resorts to force against another – the armed conflict legally continues until the general close of military operations. But it seems to me that this standard is not fitting for a situation of tit-for-tat exchanges that can be months apart. I think that a standard such as “substantial disengagement,” or something similar, might work better.  

If there is no long-standing, ongoing armed conflict between the parties, the question is whether IHL applies to each attack separately as a  “micro” armed conflict. The answer here relates to the debate on whether IHL applies to the “first shot” in an interstate resort to force. My view is that IHL should apply in such cases, because it is the better suited legal framework. It triggers the application of the legal regime of war crimes; guides combatants better in aspects such as precautionary measures; and recognizes combatant immunity which is pragmatically desirable in international armed conflict. This does not mean that International Human Rights Law (IHRL) ceases to apply alongside IHL, which might establish another level of state responsibility. It is important to stress that the fact that IHL might apply to this or that action does not make the action lawful overall if it is in violation of jus ad bellum or human rights law.        

Q-7: What, if anything, could serve to restrain the parties from further escalation at this stage?

The key to de-escalation at this specific point is for Israeli decision makers to understand that responding to Iran risks weakening the coalition of states that helped defend it against Iran’s April 13 attack. As long as this coalition holds, Iran might hesitate to pursue an escalation itself. If Israel responds aggressively to Iran’s attack it may prompt Iran to move further up the escalation ladder, and it could be more confident that the coalition would not be in place this time. The Biden administration has said it will not support an Israeli counterattack on Iran and nor would others like the Saudis who helped defend against the April 13 attack. So there is a strong risk that Israel would have to face further Iranian retaliation alone. On the other hand, if Israel responds with limited force to create a symbolic effect, it will only dilute the impact of its operational achievement in thwarting the initial attack (a very successful military operation that Israel said intercepted 99% of incoming drones and missiles). So it seems that beyond law, it’s in its best interests not to respond at this point.   

Above all, what is needed to prevent escalation in the long run are actions beyond the Israeli-Iranian conflict itself: a swift hostage deal and end to the war in Gaza with a credible “day after” vision; coupled with a political process to deescalate the situation in Israel’s border with Lebanon in line with Security Council Resolution 1701; and restoring some type of international nuclear deal with Iran.   

IMAGE: A wide view of the Security Council meeting on the situation in the Middle East. The emergency session was called at the urgent request of the Permanent Representative of Israel to the United Nations. In his letter dated April 13 to the President of the Security Council, he stated that Iran had launched “a direct attack from within its territory of more than 200 UAVs, cruise missiles, and ballistic missiles towards Israel in clear violation of the UN Charter and international law.” Similarly, the Permanent Representative of the Islamic Republic of Iran to the United Nations addressed a letter to the President of the Security Council dated April 13, asserting that the attacks were “in the exercise of Iran’s inherent right to self-defence as outlined in Article 51 of the Charter of the United Nations, and in response to the Israeli recurring military aggressions, particularly its armed attack on 1 April 2024 against Iranian diplomatic premises” in Damascus. (UN Photo/Eskinder Debebe)