A New War or a New Stage in an Ongoing War: Observations on June 13 Israeli Attack against Iran
A PDF Version of the Article for Download
Photo by REUTERS
On the night between June 12 and June 13, 2025, Israel launched a large-scale attack against numerous sites and persons in the territory of the Islamic Republic of Iran, including nuclear reactor sites, nuclear scientists, who – according to Israel – were involved in advancing the Iranian nuclear project, senior commanders of the Iranian military and Iranian Revolutionary Guard Corps (IRGC), and a number of military facilities used for storing, transporting and manufacturing surface-to-surface missiles, missile launchers, radar stations and military airfields. According to media reports, some 200 Israeli aircrafts carried out the first wave of attacks, along with unmanned aerial vehicles dispatched from secret bases inside Iran.
In its initial statement on the operation – dubbed by the IDF as “Rising Lion” – the IDF described the operation as “a preemptive, precise, combined offensive to strike Iran’s nuclear program”. According to the IDF spokesperson’s statement, Iran has come in recent months closer than ever to obtaining nuclear weapons, and this recent development, combined with repeated statements by the Iranian leadership of its intent to destroy Israel, is putting Israel under imminent existential threat. According to media reports, Israeli intelligence obtained information that, under the cover of talks with the United States, Iran was making final preparations to test the assembly of a nuclear weapon – suggesting that Israel had only a short window of opportunity to react. The Israeli ambassador to the UN also claimed that Israel had indications of Iranian plans to conduct in the near future a new attack on Israel on multiple fronts.
Initial international reactions to the new operation have been mixed. Several Middle Eastern countries have issued strong condemnations, some of which point to serious violations of international law by Israel (see e.g., UAE, Egypt and Saudi Arabia). By contrast, a number of Western countries adopted a more measured tone; some of them even reaffirmed Israel’s right to self-defense (see e.g., United States, France and Germany). In this essay, we will address the question of the legality of the use of force posed by Israel’s Operation Rising Lion. We will not address here jus in bello questions concerning targeting, such as the legality of targeting civilian nuclear scientists.
In a post on EJIL Talk!, published within hours of the attack, Marko Milanovic took the position that Israel’s operation is almost certainly illegal, since it cannot constitute an act of self-defense. His main argument is that lawful self-defense exists in international law only when the adversary’s attack had already begun or – alternatively – as an anticipatory act of self-defense against an imminent armed attack. Milanovic argued that the position according to which a State has a preventive right to self-defense against an enemy’s weapon development program that may be used against it in the future (i.e., the Bush Doctrine) has been rejected in international law. Since in the current circumstances, no Iranian attack immediately preceded the Israeli operation, nor was any evidence produced about its intentions to deliver an imminent armed attack – Israel’s attack does not meet the requirements of self-defense under Article 51 of the UN Charter, according to Milanovic.
We do not disagree with Milanovic’s analysis of the status of preventive self-defense under customary international law. If indeed, Operation Rising Lion, involves a use of force in anticipation of a non-imminent future threat – nuclear or conventional – there is good reason to deem it unlawful. This is indeed how the Security Council approached the 1981 Israeli attack against the Osirak reactor in Iraq, and this is how many mainstream international lawyers have approached the preventive defense rationale of the U.S.-led coalition 2003 invasion of Iraq. Our approach to this legal question is not affected by the growing evidence that Iran is indeed violating its obligations under the Non-Proliferation Treaty (NPT) regime (as reaffirmed by the IAEA on June 12), and that it poses a long-term existential threat to the state of Israel. Still, the critical question we discuss in this essay is whether anticipatory or preventive self-defense is the correct legal framework of analysis for the Israeli attack on Iran. As we explain below, we are of the view that another legal framework – the ongoing armed conflict framework – is more factually and legally viable than the anticipatory or preventive self-defense frameworks. In other words, it is more viable in describing the actual chain of events and in providing a legal basis for the operation.
Israel has not yet presented a clear and coherent legal argument to justify Operation Rising Lion under international law. While the reference to a preemptive strike by the IDF appears, at first glance, to point in the direction of anticipatory self-defense, as Milanovic claims, we note that the IDF statement was not articulated in legal language and did not, for example, mention the right to self-defense or Article 51 of the UN Charter. Nor did Israel submit to the UN Security Council an Article 51 notification. As a result, we contend that it can also be understood in a different way than Milanovic suggests – that is, as an attempt to justify an act of military escalation in the context of an ongoing war. Indeed, in his announcement of the Operation, Prime Minister Netanyahu referred to the future existential risks for Israel posed by Iran’s nuclear program, but also to Iran’s direct attacks against Israel in 2024 and its use of proxies against Israel in and after October 7, 2023.
The possible legal claim that Israel could make in this regard is that an armed conflict has already existed between Iran and Israel, at least since October 7 or October 8, 2023 (either on the date of Hamas or Hezbollah respectively initiating their attacks against Israel; some predate the armed conflict as far back as 2018, when Israel first attacked IRGC targets in Syria). In this armed conflict, both parties have engaged in a series of direct and indirect attacks against one another, each of which constitutes part of the same overarching armed conflict. If this description holds, then there is no need to independently justify under Article 51 of the Charter each and every distinct attack undertaken by the warring parties; however, as we explain below, there is still a need to consider the jus ad bellum necessity and proportionality of the most recent attacks (we do not address in this essay the parallel set of jus in bello issues).
The question of whether or not there exists an ongoing war between Israel and Iran has already been discussed by some authors, in connection with previous rounds of military attacks directed by the two countries against one another (see, for example, Pomson and Lieblich). In our opinion, the position that a conflict exists between Israel and Iran is a reasonable one, due to the combined effect of three related factors:
(1) Iran has surrounded Israel with several proxies as part of a national strategy to create a “ring of fire” designed to militarily weaken or even destroy Israel. These proxies have been engaged in ongoing active hostilities against Israel for at least 20 months now;
(2) Iran has directly attacked Israel on two occasions in circumstances closely related to the ongoing conflicts between Israel and Hamas, Hezbollah and the Houthis. Israel has responded to these attacks with direct attacks inside Iran;
(3) Iran has continued to issue threats of using force again against Israel intended to bring its total annihilation.
Since October 2023, a number of Iranian proxies – Hezbollah, the Houthis, and Shiite militias in Syria and Iraq – have engaged in armed attacks against Israel, intended to support Hamas in its war against Israel (we note that the links between Hamas and Iran appear to be more tenuous compared to the other organizations). While it is not clear whether the level of control exercised by Iran over each of its proxies amounts to effective control under the Nicaragua test (see para. 115), there are strong indications that it supports and exercises considerable influence over their military operations. This may suffice to regard Iran at least as “substantially involved” in the armed attacks undertaken by these groups (see GA Resolution 3314, article 3(g)), even if Israel were to be unable to directly attribute to Iran any specific attacks by its proxies (see for a discussion, Schmitt and Hernandez and Pomson). Note that according to the Nicaragua judgment, a victim State may have a right to self-defense against States substantially involved in the unlawful use of force against it (para. 195).
In addition, Iran has already chosen on two recent occasions – both related to the ongoing conflict between Israel and the Iranian proxies – to strike Israel directly with hundreds of missiles. On April 13, 2024 it conducted its first attack, in retaliation for Israel’s attack earlier that month against senior IRGC officers, who were stationed in Damascus and allegedly oversaw Hezbollah’s war effort. The second Iranian attack on October 1 was allegedly a retribution for the assassination by Israel two months earlier of Ismail Haniyeh, the head of Hamas, while he stayed in Tehran, and of Hassan Nasrallah, the head of Hezbollah, the month before. Israel has responded to its attacks with direct attacks inside Iran on April 18 and October 26. There have also been sporadic media reports of additional clandestine military operations – in kinetic and cybernetic domains – between Iran and Israel in the last 20 months. Arguably, it is possible to see the proxy war in which Iran was and remains heavily involved, and its direct clashes with Israel as two sides of the same coin – both comprising parts of the same overarching armed conflict.
Finally, public speeches and messages by senior Iranian officials suggest that they reserved for Iran the option of attacking Israel again in the context of the ongoing conflict. For example, on November 2, 2024, Ayatollah Khamanei threatened to retaliate with a “crushing response” against Israel and the United States for their actions against Iran and the “resistance front” (which is how Iran sometimes refers to its proxies). On February 21, 2025, an Iranian General, Ebrahim Jabbari, threatened that a third missile attack by Iran, which will be carried out “at the right time” will “wipe out” Israel. He also observed that the “resistance fronts” are at their peak of readiness. On May 17, 2025, Khamanei criticized Israel and the United States for bombings in Gaza and Lebanon and predicted that Israel will be “eradicated”. And, on May 26, 2025, the Army’s Commander in Chief, Abdolrahim Mousavi, threatened a “decisive strike” if Israel makes “another mistake” – a phrase which may imply an Israeli act that harms Iranian interests in a manner comparable to the harms that have led to the April and October attacks.
When viewed as a whole, we consider it somewhat artificial to neatly separate between the indirect proxy war and the direct Israeli-Iranian clashes, which emanated from the same proxy war, and between periods of direct clashes between Israel and Iran and waiting periods in which attacks “at the right time” are threatened. Such a compartmentalized and “revolving door” approach appears to obfuscate the ways in which the main protagonists see their relations with one another: Israel believes that it is confronting a seven-front war directed and participated in by Iran; and Iran adheres to the principle of “unity of fronts” (including, as one example, its direct retaliatory strike against Israel for killing the leader of Hezbollah in Lebanon). In these circumstance, we find it difficult to maintain conclusively that the test introduced by ICRC Commentary for the general close of military operations – “that the likelihood of the resumption of hostilities can reasonably be discarded” (para. 278) – has been satisfied in the Israeli-Iranian context. Although the ICRC test was introduced in the context of IHL, it influences the jus ad bellum analysis of whether the armed conflict is new or of an ongoing nature (see also here, here, and here).
In his response to comments on his post, Milanovic rejects the possibility that Operation Rising Lion was undertaken in connection with an ongoing armed conflict: “Israeli leaders have been saying, that the purpose of the use of force is to stop Iran for using nuclear weapons against Israel in the future. If that is how they describe their purpose, I fail to see why we should reorient ourselves to the supposed or real ongoing attack”. Still, as we suggest above, the framing of the operation as a preemptive strike can be regarded either as an admission by Israel that its attack is not part of an ongoing armed conflict, or an explanation for the sharp escalation of the ongoing armed conflict by Israel. We are of the view, that Israel’s consistent referral over the last 20 months to a seven-front war, which includes an Iranian front (see e.g., here and here), the lack of reference to self-defense in its June 13 statement and subsequent official statements alluding to previous Iranian attacks against Israel (see e.g., here), renders the first alternative much less plausible. We also note that in the letters Israel submitted to the U.N. Secretary General and Security Council following the direct Iranian attacks against it (see here and here), it did not directly invoke article 51 of the Charter; rather it alluded in both letters to its “right to take all necessary measures to defend itself and its citizens, in conformity with international law, against the ongoing Iranian acts of hostility, including these latest unprecedented, lawless, and malicious attacks by Iran and its proxies” (emphasis added). This appears to strongly indicate that Israel saw, at the time, these distinct attacks as part of an ongoing regional armed conflict, and not as isolated incidents.
The escalation on June 13 does raise, however, complex jus ad bellum necessity and proportionality questions, which might need to be considered based on both existing and future threats posed by Iran to Israel. We address these questions in the following section.
In another response to comments on his post, Milanovic also raised concerns about the necessity and proportionality of Operation Rising Lion: “My point is simply that [a Ukrainian attack in Russia] is nowhere near like the situation in which there’s the occasional Hezbollah or Houthi missile fired against Israel, on the assumption that these actors act on Iran’s behalf. If THAT is the ongoing armed attack by Iran, I can’t see how it could be necessary and proportionate to bomb Iranian nuclear facilities, kill the whole military leadership, attack god knows how many other targets etc”. In the same vein, it has been claimed by Kelsey Davenport in a short piece in Just Security that Israel’s action are unlikely to be effective against the Iranian nuclear sites, and they might, in fact, push Iran toward the production of nuclear weapons. The implication of these positions appears to be that even if Israel can claim, in principle, self-defense, the operation fails to meet conditions of necessity and proportionality, and is therefore likely to be rendered unlawful (we note, however, that Davenport’s analysis involves only policy considerations and the author does not draw any legal implications).
International law scholarship on the question of how to apply Jus ad Bellum necessity and proportionality conditions to an ongoing armed conflict is not consistent. On one end of the spectrum, Yoram Dinstein has claimed (at p. 57) that necessity and proportionality govern only the initial decision to use force in response to an armed attack. According to Dinstein, there is no need to examine the jus ad bellum necessity and proportionality of each subsequent attack occurring during the armed conflict. This position seems to enjoy general support in State practice. The more dominant position that is found in the contemporary literature, however (see e.g., here, at p. 17) – which we also find preferable – is that necessity and proportionality have to be assessed throughout the conflict, and that attacks that are jus in bello lawful may still run afoul of jus ad bellum since they are unrelated to, or are excessive in relation to the legitimate aims of the relevant self-defense operation.
Furthermore, there is also a well-known doctrinal disagreement surrounding the scope and nature of the legitimate aims of self-defense – in particular, whether defending states can go beyond halting and repelling the attack carried out against them and address the risk of future attacks (see e.g., Kretzmer and Nolte). We are of the view that if the proxy war and the direct Israeli-Iranian hostilities are intertwined (for the reasons explained above), then even under the narrow halting and repelling test, Israel is entitled to take self-defense measures against Iran, since some of its proxies – Hamas and the Houthis – continue to launch rockets against Israel almost on a daily basis with Iran’s substantial involvement.
The more difficult legal question, we believe, pertains to proportionality analysis. Admittedly, there is a tension between the declining number of Iranian proxies directly involved in the war against the Israel and the overall firepower they maintain, and the significant escalation of the Israel-Iranian conflict through the launch of Operation Rising Lion (we note, however, that Iran’s threats to deliver a “crushing response” to Israel persisted and that, when viewed in its entirety, very high levels of force have already been applied against Israel throughout the seven-front war).
The key facts for the proportionality analysis pertain, we believe, to the evolving nature of the Iranian threat: If an Iranian escalation was expected in the near future (as alleged by the Israeli Ambassador to the UN), it can be claimed that some degree of preemption should be tolerated even under the narrow approach to jus ad bellum proportionality, as applied to an ongoing armed conflict, and even if such escalation was not imminent. In other words, we maintain that the temporal boundaries of preemption should be applied in a more flexible manner within the context of an ongoing war of self-defense than in relation to a new armed conflict, where a right to self-defense does not exist yet. An alternative position, according to which even during an ongoing armed conflict a state has to wait for escalation by its adversary before responding more forcefully in anticipation of such escalation appears to us to be untenable and completely unsupported in State practice (to the contrary, surprise offensives play an important role in military doctrine, including in wars of self-defense. See e.g., here). Note that this debate is similar to other discussions in jus ad bellum, where legal commentators argue that States cannot justify an initial attack on another States on the basis of “deterrence”. Whether that’s true or not, surely such a restriction does not apply in the same manner to military operations once the armed conflict is well underway.
What’s more, it is difficult to accept that defending States should remain indifferent to significant changes in the nature of the threat posed to them by their adversaries during an ongoing armed conflict. In cases where dramatic changes in risk levels occur, it is reasonable to respond (even under a halt and repel standard) in a manner that also considers the future threat that the continuation of attacks poses to the victim State (for a discussion of interconnected dual claims, relating to past and future attacks, see Green at pp. 34-37; for a discussion of reasonableness in application of jus ad bellum proportionality, see Greenwood, at p. 223). This is especially true in circumstances where the prospects of a subsequent Security Council intervention in the ongoing armed conflict are low.
We are of the view that this should be the proper context to evaluate Israel’s preemptive strike claim – it has chosen to escalate the existing armed conflict with Iran because its risk evaluation and sense of urgency has radically changed. In the weeks before Operation Rising Lion, Israel allegedly obtained information that Iran is moving very close toward assembling a nuclear bomb (a development that must be considered in view of Iran’s repeated threats to eradicate Israel), the IAEA found Iran to be in violation of its NPT obligations, and the prospects of an effective US-Iran deal on Iran’s nuclear program have dimmed. Arguably, the serious nature of these developments could justify a powerful preemptive attack during an ongoing armed conflict. As for the timing of the attack, we note that it seems to have also been dictated by a unique combination of military and political considerations – among them, the severe weakening of Iranian air defense capacities in the Israeli attack in October (which created an operational window, until the damaged systems would be restored), the incapacitation of Hezbollah – Iran’s main proxy – which reduced the risk of overwhelming retaliation, and the expiration of the 60 day timeline given by President Trump to Iran to negotiate a deal.
Another claim raised against Israel – which might affect the jus ad bellum necessity and proportionality analysis – is that the force applied in Operation Rising Lion is not effective, since it does not appear to have the actual capability to destroy the Iranian nuclear program. While this may be a valid criticism of the military and political wisdom of launching the operation, we do not believe that international law doctrine conditions the right to self-defense on the defending side’s prospects of success. Were we to follow this logic, Poland would not have had the right to self-defense against the 1939 attack by Nazi Germany because it was perfectly clear that the Germans would win the war between the two States. In fact, the information published so far about the Israeli operation inside Iran suggests that some of Israel’s objectives – downgrading Iranian missile capabilities, eliminating the top military leadership – could have already been achieved. It is also possible that the operation would prove effective in delaying Iran’s nuclear program, or in inducing it to show more flexibility in its negotiations with the United States. The negative verdict also seems somewhat premature. The operation is still ongoing, with Israel still increasingly achieving its military goals.
Whereas Milanovic reviewed the legality of Operation Rising Lion, launched by Israel on June 13, under an anticipatory self-defense framework and found it to be almost certainly unlawful on those grounds, we are of the view that a more appropriate framework may be the legality of escalation in an ongoing armed conflict. We claim, in this regard, that the significant links between Iran and its proxies in the war launched against Israel on October 7, 2023, the past rounds of direct clashes between Iran against Israel, which were closely connected to the proxy war, and Iran’s continuing threats to strike Israel again, support the proposition that Israel and Iran have been engaged for an extended period in an ongoing armed conflict (which Israel regards as a seven-front war). Israel’s initial reference to the operation as preemptive in character is not determinative of the legal analysis, since the qualification is relevant to the legal analysis under both competing frameworks – anticipation and escalation.
Under the ongoing armed conflict framework of analysis, we maintain that even those (like us) who believe that jus ad bellum necessity and proportionality conditions continue to apply throughout different stages of an armed conflict, should allow for some flexibility in the application of the right to self-defense to future new threats of a serious nature, evolving in the midst of a conflict. Hence, less than imminent threats may also be responded to in this context, and emerging threats – especially non-conventional in nature – may change the proportionality analysis. To be clear, we certainly do not endorse a general right to preventive self-defense, and our position is limited to new threats arising during an ongoing armed conflict. The upshot of our analysis is that a categorical finding that Israel almost certainly violated international law in conducting its attack against Iran seems to us dubious or, at least, premature in nature. A more definitive analysis would require, we believe, more information on the nature of relations of Iran and its proxies and Iran’s substantial involvement in the regional war, as well as on the temporal and other elements of the risk analysis, which underlaid Israel’s decision to escalate the conflict. We realize, however, that much of this information is classified in nature and is unlikely to be fully revealed anytime soon.
The authors thank Ms. Tal Gross for her comments on an earlier draft.
This article was published in Just Security