Select IHL Issues Arising from the Israel-Iran Conflict

The Israeli strikes on Iran on 13 June 2025 and the ensuing attacks from both sides have raised important questions of international law. Several questions concern the legal basis under the ius ad bellum for the initial Israeli attack. This issue has been addressed by various commentators, including here, here and here.

Much less attention has so far been paid to issues concerning the application of the ius in bello or international humanitarian law (IHL). This is somewhat surprising, because the fighting raises interesting questions from this perspective. This post aims to discuss a number of these questions, without necessarily providing a conclusive answer.

A Pre-Existing Armed Conflict?

A first question concerns the application of IHL. There is little doubt that the initial Israeli attack triggered an international armed conflict (IAC) between Israel and Iran. The use of force employed by Israel clearly meets the test set out in the Tadić judgment by the Appeals Chamber of the International Criminal Tribunal for the former Yugoslavia (ICTY) for the existence of an international armed conflict, namely that there is “resort to armed force between States.”

This is certainly the case if one adheres to the so-called “first shot” theory, under which the threshold for an IAC is very low. This interpretation finds broad support in the literature and is also advanced by the International Committee of the Red Cross (ICRC). Another view, which finds some support among commentators (see e.g. Gill), considers that a de minimis threshold of force must be crossed for an IAC to be triggered. The large-scale operation by Israel on 14 June, however, appears to easily meet even this stricter test.

An interesting question is whether IHL governed the first attack by Israel. This question has been debated intensively by a number of scholars, including in the context of the killing of Iranian General Soleimani in 2020. One set of commentators argued, or at least suggested, that the first blow triggers an armed conflict and the application of IHL, but is not itself regulated by that legal regime (see e.g. Heller).

Another set of commentators defended the view that the initial attack that triggers the application of IHL is itself already governed by IHL. The idea behind this view seems to be that IHL applies as soon as an attack (as that term is used in IHL) is initiated. Everything that follows that initiation would then be regulated by IHL. In my view this position is the more convincing one. As Lieblich states, there is ample space to argue that IHL indeed applies from the commencement of the very first inter-State attack (and not only after its kinetic impact), and there are also strong normative arguments for this position.

This question would be moot however if it was concluded that there was a pre-existing IAC between Israel and Iran. This could be either because earlier uses of force between Israel and Iran triggered an IAC that continued until 13 June and/or because an armed conflict between Israel and one or more organized armed groups supported by Iran (Hamas, Hezbollah, Ansar Allah) was “internationalized.”

With respect to the existence of a pre-existing IAC based on a previous use of force between Israel and Iran, there is no doubt that such use of force has occurred. The latest manifestation of this was an Iranian attack in October 2024, when Iran fired around 200 ballistic missiles at Israel. Iran claimed that the attack was an act of retalation for Israel’s assassinations of Hamas leader Ismail Haniyeh in Tehran, Hezbollah leader Hassan Nasrallah, and Iranian Revolutionary Guard Corps general Abbas Nilforoushan. On 26 October 2024 Israel launched strikes in Iran in response, which caused extensive damage to Iran’s air defence systems, thus facilitating the later strikes of 13 June 2025. There is little doubt that this triggered an IAC. The question is whether this conflict had ended and if so, when.

Many commentators agree that an IAC ends when there is a “general close of military operations.” This standard is taken from Article 6 of the Fourth Geneva Convention. There seems to be broad support for the view, put forward by the ICRC and a number of authors, that the general close of military operations presupposes that “the likelihood of the resumption of hostilities can reasonably be discarded.” On a broad reading of this requirement, there might be a plausible argument that an IAC continued to exist after the October 2024 exchanges of fire. Indeed, in December 2024 it was argued that this was still the case.

There are indications that Iran continued to carry out military preparations on its own territory with a view to further hostilities with Israel and vice-versa (see e.g. here and here). I have doubts, however, whether such a broad interpretation of the standard for the end of an IAC is justified. In the case of Iran and Israel, no actual hostilities had occurred for more than six months after the October 2024 exchanges. Arguing that there was still an IAC would set the bar for the continuation of an armed conflict very low, a view which would be difficult to square with the exceptional nature of armed conflict.

Alternatively, it could be argued that the ongoing conflict between one or more of the organized armed groups supported by Iran was internationalized due to Iran’s support. The threshold for such internationalization would be the exercise of “overall control” by Iran over such a group or groups. This standard was set out by the ICTY Appeals Chamber in the Tadić case and now enjoys broad support.

Ultimately, whether the case of Iran and Israel met this standard depends on the facts of relationship between Iran and the groups supported by Iran. These are not clear based on publicly available information. So far, no conclusive evidence has emerged to suggest that Iran exercises overall control over any of these groups and until it does, it must therefore be concluded that the existing non-international armed conflicts between Israel and these groups have not been internationalized. This is a view that is also shared by various commentators not (see inter alia here and here).

Attacks on Nuclear Sites

Israel’s attacks were partly aimed at infrastructure that Israel claims Iran used to develop a nuclear weapons program. It was therefore to be expected that nuclear fuel was present there, which could be especially dangerous when attacked. The International Atomic Energy Agency has already warned that there is a risk of a radiological release when such attacks are carried out.

Under IHL, only one treaty obligation specifically protects nuclear installations. Article 56 of Additional Protocol I (AP I) provides that “works or installations containing dangerous forces, namely dams, dykes and nuclear electrical generating stations, shall not be made the object of attack.” The specific reference to “nuclear electrical generating stations” suggests that other nuclear facilities that do not generate electrical power fall outside its scope of application. Some have argued that the list of installations in the article is illustrative and not exhaustive (p. 149). This seems to contradict the clear text of the article however, which uses the term “namely.” The better view therefore is that nuclear facilities other than nuclear power plants fall outside of the scope of Article 56. In any event, Israel is not a party to AP I and therefore it is not bound by this article.

The general IHL rules of targeting would apply to any attack by Israel, however. Thus, an attack on a nuclear site must satisfy the critera for a military objective. There is broad agreement that the test set out in AP I, Article 52 reflects customary law in this respect. Under this test arms and munitions factories are generally considered to constitute legitimate military targets. It would not be a stretch to argue that facilities developing weapons would also be lawful targets. For this to be the case, however, the facilities attacked must actually be involved in such development. This is something that Iran has denied.

If the nuclear facilities targeted by Israel constituted legitimate military objectives, attacks would still be subject to the principle of proportionality and the duty to take precautions in attack. In terms of proportionality, it can be argued that neutralizing the construction of nuclear weapons offers a significant military advantage. On the other hand, the potential for serious civilian harm arising from radiological release must be taken into account in considering the expected civilian harm. It was reported that Israel did not strike Iran’s Fordo nuclear site for fear of triggering radiological fallout.

Attacks on Nuclear Scientists

The Israeli attacks also targeted a number of nuclear scientists, a claim Israel has not denied. In a press release of 14 June, the IDF stated that nine senior scientists and experts, who advanced the Iranian regime’s nuclear weapons program, were eliminated. A day later it was reported that at least 14 nuclear scientists had been killed. No claims indicate that the scientists concerned were members of the armed forces of Iran. If they were, they would have been combatants and as such legitimate targets at all times. If they were civilians, as appears to be the case, they would in principle be protected from direct attack.

They would lose this protection only if they were “directly participating in hostilities” (DPH). This exception to the protection of civilians from attack is set out in AP I, Article 51(3) and broadly recognized as reflecting customary law. Notoriously, IHL treaty law does not contain a definition of DPH. The ICRC published its Interpretive Guidance on DPH in 2009, following a number of meetings with experts. Based on this interpretation, nuclear scientists would generally not lose their protection from attack as the requirement of “direct causation” would not be met. Indeed, the Guidance explains that participation in the general war effort does not constitute DPH, and that this includes “design, production and shipment of weapons and military equipment.”

Although the ICRC’s interpretation is authoritative, it is considered too strict by a number of States and commentators. In the Targeted Killings case before the Israeli High Court of Justice, President Barak of the Court took a broad approach to the definition of DPH. However, he did not address the situation of civilian scientists. The case of such scientists was discussed during expert meetings organized by the ICRC on the issue of DPH leading up to the publication of its Interpretive Guidance. In particular, several experts addressed the issue during the fourth expert meeting in 2006.

During this meeting, one expert raised the question whether “civilian specialists possessing expertise on decisive new means or method of warfare” could be considered to be directly participating in hostilities. In response, “several experts insisted that there has been a consensus since the Second World War that neither armament industry employees, nor nuclear weapons experts, were considered to be directly participating in hostilities regardless of their value to the war effort” (p. 49). During the same discussion, another expert agreed with the principle that,

a civilian weapons expert should not lose protection against direct attack, [but] nevertheless doubted whether this assessment could be maintained in extreme situations where the expertise of a particular civilian was of very exceptional and decisive value for the outcome of an armed conflict. For example, in the case of nuclear weapons experts during the Second World War, the enormous importance of the individual contribution to the war effort clearly exceeded the ordinary and could perhaps have lead to a conclusion deviating from the general rule (p. 49).

Based on this exchange, it appears that the majority view of legal experts was that nuclear scientists would not lose protection from attack. With regard to the statement of the expert who referred to the case of the Second World War, it may be pointed out that arguably, the contribution of individual scientists in the current day is not comparable to the contribution of, for example, Robert Oppenheimer some 80 years ago.

Conclusion

The fighting between Israel and Iran not only raises important issues of ius ad bellum, but also questions concerning the application of IHL. There is no doubt that IHL applies to the hostilities after the initial Israeli strikes, and this post argued that it applies also to the very first strike. Nuclear facilities could constitute legitimate military targets, if they were indeed being used to develop a nuclear weapon. Attacking them would however be subject to the principles of proportionality and precautions. With regard to attacks on nuclear scientists, these seem constitute a violation of IHL because the scientists were civilians who were not directly participating in hostilities.

***

Marten Zwanenburg is Professor of Military Law at the University of Amsterdam and at the Faculty of Military Sciences of the Netherlands Defence Academy. He has previously worked as a legal counsel for the ministries of Defence and Foreign Affairs of the Netherlands. 

The views expressed are those of the author, and do not necessarily reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.

Articles of War is a forum for professionals to share opinions and cultivate ideas. Articles of War does not screen articles to fit a particular editorial agenda, nor endorse or advocate material that is published. Authorship does not indicate affiliation with Articles of War, the Lieber Institute, or the United States Military Academy West Point.

Photo credit: Avash Media