Evaluating Israel’s Strikes in Iran

It has been argued that Israel’s “Operation Rising Lion” cannot be justified under jus ad bellum, because it fails the necessity and proportionality criteria for self-defense. This post contends that such analysis misapplies standards. An international armed conflict (IAC) exists between Iran and Israel since at least April 2024’s direct Iranian attack, or arguably since the 1979 revolution and the ensuing decades-long proxy war. Given the existence of an IAC, Israel’s strike must be primarily analyzed under jus in bello. Alternatively, Israel’s strike meets the criteria for preventive self-defense given Iran’s nuclear and ballistic missile threat.

Context of the “Operation Rising Lion”

On 17 June 2025, Israeli Foreign Minister Gideon Sa’ar’s UN Security Council letter outlined Israel’s basis for the operation, targeting Iran’s nuclear and ballistic missile programs as existential threats. Israeli intelligence noted Iran’s acceleration toward nuclear weapons and an arsenal of close to 10,000 ballistic missiles. Iran had launched hundreds of rockets at Israel, an intolerable risk given Israel’s size. Sa’ar highlighted Iran’s annihilation threats, its “ring of fire” strategy, and global terror attacks against Israeli and Jewish targets.

Existence of an Armed Conflict between Israel and Iran

Both Israel and Iran understand themselves to be in a long-standing war, often clandestine or through proxies. As such, “Operation Rising Lion” should be seen as another stage in the Iranian-Israeli armed conflict. As the ICTY Appeals Chamber in Tadić stated, “an armed conflict exists whenever there is resort to armed force between States” (para. 70). According to the ICRC Commentary on Common Article 2 of the Geneva Conventions, the question “how much slaughter takes place” is not relevant to whether an IAC exists; and, even if there is “only a single wounded person as a result of the conflict”, the law of armed conflict applies (ICRC Commentary of 1952; see also Dinstein, Non-International Armed Conflicts in International Law, p. 51).

On 13 April 2024, Iran launched its first direct attack on Israel, sending around 170 drones, 30 cruise missiles, and 120 ballistic missiles towards Israel. The strike has been called the most significant attempted drone attack in history and, in a continuation of the IAC, followed an airstrike by Israel on officers of the Islamic Revolutionary Guard Corps (IRGC) and two Syrian civilians attached to the Iranian embassy complex in Damascus, Syria. One Israeli civilian was critically injured, and 31 other civilians were treated for minor injuries or post-traumatic stress. On 1 October 2024, Iran launched 200 ballistic missiles at Israel in two waves. The attack killed one Israeli civilian and one Palestinian civilian, as well as causing significant damage to Israeli homes.

A temporary lull in hostilities does not necessarily mark the end of an armed conflict. Dinstein, for example, justifies Israel’s 1981 strike on the Iraqi nuclear reactor based on the state of hostilities that persisted between the two countries since the 1948 war. Israeli and Iraqi armed forces fought against each other in June 1967 and October 1973. Iraq launched Scud missiles at Israeli population sites in 1991 (War, Aggression and Self-Defence, p. 45). Dinstein likewise justifies the 2007 Israeli strike on a Syrian nuclear installation on similar grounds (ibid., p. 199).

The ICRC Commentary considers an armed conflict closed when “the likelihood of the resumption of hostilities can be reasonably discarded” (para. 278). In the past several months, both Israeli and Iranian leaders have issued statements indicating the opposite, a continuation of hostilities. In October 2024, the IRGC stated that “if the Zionist regime reacts to Iranian operations, it will face crushing attacks”. On 8 May 2025, Israeli Defence Minister Katz warned: “What we did to Hezbollah, Hamas, Assad, and the Houthis, we will do to you as well in Tehran”. On May 26, 2025, the Iranian Army’s Commander in Chief, Abdolrahim Mousavi, threatened a “decisive strike” if Israel makes “another mistake”.

Attribution of Hamas, Hezbollah, and Houthi Attacks to Iran

Attributing proxy attacks to Iran strengthens the case that an IAC has been ongoing for decades. More directly, the attack of 7 October 2023 can be credibly understood as an Iranian use of force against Israel.

UNGC 3314 recognizes “substantial [State] involvement” in armed group attacks as an “act of aggression” (Article 3(g)). Iran’s training and provision of weapons to armed groups certainly meet the standard of “substantial involvement”. Scholars such as Tom Ruys and Carsten Stan have argued that “substantial involvement” must be understood consistently with “overall control” criteria (see Flasch).

The ICTY’s Tadić “overall control” test criteria are: equipping, financing, and coordinating military activity suffice, without specific act instructions (para. 131). Other factors include organization, training, equipping, operation planning, target selection, and support (para. 112).

Iran’s involvement with Hezbollah, Hamas, and the Houthis meets this standard. Regarding Hezbollah, the IRGC has, since the 1980s, provided the organization an arsenal of 120,000 to 200,000 rockets/missiles as well as funding and training. IRGC Brigadier Zahedi sat on Hezbollah’s Shura Council and Iran further supplies intelligence for attacks. For Hamas, 500 militants were trained in Iran by the Quds Force before the 7 October attacks. Hamas’ tactics, including the use of drones and motorcycles, mirror those employed by Iranian forces. Furthermore, IRGC coordinated with Hamas/Hezbollah for months, approving the attack in Beirut which was praised subsequently by Khamenei as a “decisive blow”. The Iranian news network Tasnim detailed four years of training. Finally, the Houthis similarly receive Iranian arms and guidance.

Iran sees Hamas, Hezbollah, the Houthis, and other militias as members of the “Axis of Resistance”, sharing a coordinated strategy to destroy Israel. Israel similarly sees itself in a seven-front war, with Iran as “the head of the snake”. Corn notes Iran’s Hezbollah control meets Tadić, making Iran an IAC party since at least April 2024.

Primacy of Jus in Bello over Jus Ad Bellum to Assess Recent Strikes

Having established that Israel and Iran have been engaged in an ongoing armed conflict, this contribution argues that the legality of Israel’s “Operation Rising Lion” should be assessed under jus in bello rather than jus ad bellum. As part of an ongoing armed conflict, Israel’s recent strikes in Iran cannot be considered a retaliatory action. According to the United States’ official position as articulated by former State Department Legal Adviser Brian J. Egan, once self-defense is initiated against an armed group, no repeated imminence reassessments are needed if hostilities continue.

Professor Geoffrey Corn shares this view. Dinstein, similarly, states that jus ad bellum proportionality and necessity no longer apply when an aggrieved state is at war. “Once the war is raging, the exercise of self-defence may bring about ‘the destruction of the enemy’s army’, regardless of the jus ad bellum condition of proportionality” (War, Aggression and Self-Defence, p. 208).

To add further nuance to Egan’s explanation, the United Kingdom’s position, as outlined by Attorney General Jeremy Wright in his 2017 speech on “The Modern Law of Self-Defense,” offers a complementary yet more restrictive framework for evaluating self-defense in ongoing conflicts. The multi-factor imminence test (threat nature, pattern, harm scale, last chance) aligns with Egan, who argues that a new imminence assessment is not required for every use of force in an armed conflict, requiring evidentiary standards but rejecting broad preemption. In Israel-Iran, proxy patterns and nuclear acceleration support no constant jus ad bellum reevaluation.

It is acknowledged that the above-mentioned position remains contested. Some critics argue that the principles framing the use of force between states, such as the necessity and proportionality jus ad bellum requirements, continue to be relevant during ongoing armed conflicts and must be regularly assessed, requiring separate justification for significant escalations like targeting nuclear assets (as addressed here, here, and here). Additionally, the US and UK practice may not reflect the view of the majority of states, though they represent major powers with extensive practice in such matters.

State practice, like treating Russia’s 2022 Ukraine invasion as a jus ad bellum violation despite 2014 hostilities, suggests major force requires separate jus ad bellum assessment. But this differs: Russia is the aggressor while Israel is the victim of Iran’s proxies (e.g., October 7, 2023) and direct strikes (April/October 2024). The requirement for a new jus ad bellum analysis for an Israeli response would favor the aggressor party. It is unlikely that Ukraine would be required to make a new jus ad bellum assessment if it were to launch a major operation against Russia.

Additionally, Israel’s strikes appear to comply with the principles of jus in bello, as they targeted legitimate military objectives, including Iran’s nuclear and ballistic missile facilities, which posed imminent threats and were critical to Iran’s military capacity. Although this question too is subjected to vigorous debates (see here and here), there is room to claim that the strikes adhered to the principle of distinction by focusing on IRGC officials and nuclear scientists directly involved in hostilities, while proportionality was maintained, with incidental civilian harm (approximately 224 deaths, mostly near military sites) outweighed by the military advantage of neutralizing existential threats. Israel’s use of precise intelligence, evacuation warnings, and precision-guided munitions fulfilled the obligation of precautions, fostering compliance with international humanitarian law.

Justifications under Jus Ad Bellum

Even under the framework of jus ad bellum, Israel’s “Operation Rising Lion” would be lawful under international law. As previously stated, Israel had two explicit military objectives: a preventive strike against Iran’s nuclear facilities, as well as a preventive strike against Iran’s ballistic missile program. Israel’s military and security chiefs all advised the political echelon that Israel had a brief window to act against Iran.

The unique characteristics of the use of nuclear weapons are highlighted by the ICJ Advisory Opinion about the Legality of the Threat or Use of Nuclear Weapons. It states those “unique characteristics of nuclear weapons”, which include “in particular their destructive capacity, their capacity to cause untold human suffering, and their ability to cause damage to generations to come” (para. 36) are relevant when assessing whether a preventive right of self-defense exists. As Israel stated in its letter to the UNSC, Iran escalated its nuclear enrichment program in recent months. In a December 2023 report, the IAEA said that Iran was now producing a higher level of enriched uranium that could quickly be upgraded to weapons-grade levels. According to Israeli intelligence, Iran was only a short period away from being able to produce nuclear weapons.

According to a recent Times of Israel report, Iran had accelerated its ballistic missile program, amassing 2,500 potent missiles (many with 1-ton warheads) and projecting 4,000 by March 2026 and 8,000 by 2027. This escalating conventional threat risked overwhelming Israel’s defenses, inflicting untenable destruction, and preventing effective military response – especially if combined with drones targeting air bases to ground the air force. The Caroline criteria require anticipatory self-defense to meet the conditions of necessity and proportionality. These criteria are considered as the basis of anticipatory self-defense under customary international law.

The Six-Day War of 1967 provides a historical precedent for anticipatory self-defense under similar conditions. In May and June 1967, Egypt, Syria, and Jordan amassed troops along Israel’s borders, closed the Straits of Tiran (a critical economic lifeline), and engaged in bellicose rhetoric threatening Israel’s destruction. While no attack had yet occurred, the combination of military mobilization, strategic encirclement, and explicit threats created a situation where Israel’s leadership deemed preemptive action necessary to prevent an existential threat. On 5 June 1967, Israel launched a preemptive strike, which was widely debated but ultimately considered by many legal scholars to meet the Caroline criteria due to the immediacy and severity of the threat.

Like the Six-Day War, “Operation Rising Lion” addresses a complex threat: Iran’s near-weapons-grade nuclear enrichment and its expanding ballistic missile arsenal, risking Israel’s defenses. In both cases, the necessity criterion is met because waiting for the enemy to strike first would have catastrophic consequences – whether from a coordinated Arab invasion in 1967 or a nuclear-armed Iran with thousands of missiles in 2025. The proportionality criterion is satisfied, as Israel’s strikes targeted specific military objectives (nuclear facilities and missile programs) to neutralize the threat without excessive force.

Conclusion

The persistent armed conflict between Israel and Iran – traced back decades or at least to April 2024 – requires assessing Israel’s actions under jus in bello principles (necessity, distinction, proportionality, precaution) rather than jus ad bellum. Once underway, operations need no per-action self-defense justification if hostilities persist, aligning with views that jus in bello governs independently of jus ad bellum proportionality. Alternatively, under jus ad bellum, Iran’s accelerated nuclear enrichment and missile programs compelled immediate, overwhelming Israeli response.