Israel’s attacks on Iran’s nuclear weapons program, which began early Friday, June 13, are lawful, contrary to the expressed views of various commentators and politicians, including Senator Bernie Sanders.
Several of these commentators have based their contention that Israel’s attack is illegal on their opinion that Israel was not responding to an “imminent” nuclear attack by Iran. But this argument overlooks a critical legal principle: When two countries are already in a state of armed conflict—in colloquial terms a war—there is no requirement to wait for “the next attack” to be imminent.
Israel’s attack on Iran’s nuclear weapons program, including its ballistic missile capabilities, was legal because Iran and Israel were already engaged in an ongoing international armed conflict. Furthermore, even assuming for argument’s sake that this was not the case, the imminence test was met by the facts in place on June 12, fully justifying Israel’s invocation of the international legal right for a state to defend itself against an imminent unlawful armed attack.
The armed conflict between Iran and Israel has been ongoing since at least April 13-14, 2024, when Iran fired over 300 drones and missiles at Israel and, in the view of some experts, even prior to this date as the result of attacks against Israel by Iran’s main proxy, Hezbollah. Then, on October 1, 2024, Iran launched at Israel over 180 missiles, reportedly the largest ballistic missile attack in history. In late May 2025, Major General Abdolrahim Mousavi, commander-in-chief of Iran’s army, threatened another similar missile attack against Israel to “collect on what they already owe us.”
While an armed conflict continues, there is no requirement to justify every attack against the enemy through the pre-war imminence test. With Iran already engaged in ongoing conflict with Israel, international law did not require Israel to wait to take military action against these vital enemy assets until just before Iran either launched a nuclear missile against Israel or otherwise fired its proverbial next shot. Instead, it was legal, as well as logical, that Israel attack the enemy’s most dangerous weapon system—in this case, Iran’s nuclear weapons program.
Those arguing Israel acted prematurely to defend itself ignore the fact that Israel’s right of self-defense was first triggered when Iran initiated this armed conflict in April 2024. The assertion that the armed conflict essentially terminated after the October 2024 round of Iranian missile attacks against Israel is misguided. Iran’s eliminationist threats and actions towards Israel, coupled with its relentless march towards nuclear weapons—not to mention the continuation of the ‘shadow war’ between the two countries that predates Iran’s missile attacks—invalidates such an assertion.
Wars do not progress on a flatline of intensity, and attacking enemy military targets when and where one is most likely to achieve maximum military advantage is both legal and logical in war. Suggesting that imminence of another Iranian attack, either nuclear or conventional, was a necessary condition for this military campaign against Iran ignores the international law governing ongoing armed conflict.
This approach to assessing the legality of attacks is a longstanding cornerstone of U.S. policy. Brian J. Egan, while serving as State Department legal adviser under President Barack Obama, explained that, “In the view of the United States, once a State has lawfully resorted to force in self-defense against a particular armed group following an actual or imminent armed attack by that group, it is not necessary as a matter of international law to reassess whether an armed attack is imminent prior to every subsequent action taken against that group, provided that hostilities have not ended.”
In addition, Paul Ney, the DOD general counsel during the first Trump administration, noted in relation to the attack that killed Islamic Revolutionary Guard Corps commander Qasem Soleimani that “an imminent attack is not a necessary condition for resort to force in self-defense in this circumstance because armed attacks by Iran already had occurred and were expected to occur again.”
This rationale for attacking a nuclear weapons program facility during an ongoing armed conflict should resonate with Iran, which, during the Iran-Iraq War, itself conducted an airstrike on Saddam’s Osirak nuclear reactor.
Even if Iran were not in an ongoing armed conflict with Israel, Israel would have had the right, under the current circumstances, to destroy Iran’s nuclear weapons program as an act of self-defense. Defending against an Iranian nuclear attack would be nearly impossible once that weapon was developed and fielded. It was therefore reasonable for Israel’s leaders to conclude that launching last Friday’s attack was the last feasible opportunity to prevent Iran from acquiring a nuclear weapon it could use to fulfill its vow of destroying Israel.
Iran’s leaders have repeatedly expressed an intent to “annihilate” Israel. Iran’s Supreme Leader, Ayatollah Ali Khamenei, last month said Israel “is a lethal, dangerous, cancerous tumor [that] should certainly be eradicated, and it will be.” In celebration of Iran’s October 1, 2024, missile attack against Israel, Tehran erected a giant billboard declaring “Israel must be wiped off the face of the earth.” In addition, the commander of Iran’s Revolutionary Guards, Major General Hossein Salami, killed during Israel’s attack on June 13, said Israel “must be wiped off the map and this is no longer . . . a dream (but) it is an achievable goal.”
Underscoring the connection between Iran’s nuclear program and the Iranian leadership’s threats to destroy Israel, Iran has both displayed and launched ballistic missiles emblazoned with the words “Israel must be wiped off the face of the Earth” and “Death to Israel.” Iranian military parades have repeatedly featured Shihab-3 missiles draped in banners containing the Persian language slogan “Israel must be destroyed.” The International Atomic Energy Agency (IAEA) has reported evidence that Iran has worked to develop a nuclear warhead for the Shihab-3 missile—a weapon that can already reach Israel.
By June 12, 2025, Iran’s nuclear weapons program had crossed the proverbial Rubicon. Current and former Iranian officials had stated that Iran’s nuclear weapons program was close to fruition. One even hinted that Tehran already had all the pieces needed to assemble its warhead. A recent study, which one of us co-authored, indicated Iran’s breakout time was down to a mere week. Meanwhile, United States and Israeli intelligence discovered that Iran had accelerated its efforts to build a nuclear trigger.
The IAEA’s June 12 resolution determined that Iran was in “non-compliance” with its nuclear nonproliferation legal obligations and warned of “the rapid accumulation of highly enriched uranium by Iran.” The resolution concluded that, after more than twenty years of dialogue, IAEA efforts to persuade Iran to change course were “at an impasse.”
The IAEA resolution provided a list of steps that are “essential and urgent” for Iran to take “without delay” to “urgently remedy its non-compliance.” Iran responded not by taking these steps to end its violations but rather by announcing a drastic new acceleration of its nuclear weapons program.
At that point, peaceful efforts to ensure Iran fully complied with its nonproliferation obligations—to include the Trump administration’s efforts at negotiation—were indeed “at an impasse,” as the IAEA resolution described the situation. Rather than engage constructively in negotiations with the IAEA and the United States, Iranian leaders exploited the talks to provide cover while racing ahead towards a nuclear arsenal.
Assertions that the nuclear threat to Israel was not yet imminent, and that Israel should have ignored Iranian threats to destroy it, overlook the gravity of the risk Israel faced. Sir Daniel Bethlehem, former principal legal adviser to the United Kingdom’s Foreign and Commonwealth Office, highlights gravity of a threat as a factor in imminence assessment in his highly influential 2012 article. His approach arguably became a cornerstone of the so-called Obama doctrine on using force in self-defense, and has been reflected in U.S. practice ever since.
Some may assert that Israel’s impressive counter-missile capabilities lessen the gravity of the threat Israel faced. But planning for a defensive capability to be totally effective is planning to fail, as has been proven many times throughout history.
One need only consider the footage of Iranian conventionally-armed ballistic missiles that have already penetrated Israel’s air defense umbrella to appreciate precisely why it would be folly to over-rely on this defensive shield. More importantly, Iranian success to date increases the gravity of risk inherent in delaying this campaign. Imagine if even one of those missiles had carried the nuclear warhead Iran was so determined to field.
Some have also argued that international law prohibits any attack directed against nuclear facilities, no matter the circumstances. This mistaken idea may stem from a misunderstanding of Article 56 of Additional Protocol I (API) to the Geneva Conventions of 1949.
Article 56 prohibits attacks only on one type of facility, “nuclear electrical generating stations,” and only if such attacks “may cause the release of dangerous forces and consequent severe losses among the civilian population.” The Bushehr nuclear power reactor is the only facility in Iran that falls within the ambit of Article 56. Israel has not attacked Bushehr, which is considered of much less proliferation concern than several other Iranian nuclear facilities.
The top targets for Israel’s attack on Iran’s nuclear program are Iran’s Fordow and Natanz enrichment facilities, Arak heavy water plant, and Isfahan uranium conversion facility. Article 56 does not restrict parties to the API from attacking enrichment facilities, heavy water plants, or uranium conversion facilities. In any event, Israel, like the United States, as well as Iran, has chosen not to become a party to the API, is not bound by it, and does not consider Article 56 a reflection of customary international law.
Similarly, commentators have also cited the following non-binding opinion which the general conference of the IAEA board of governors has expressed on at least three occasions (including in September 2009): “any armed attack on and threat against nuclear facilities devoted to peaceful purposes constitutes a violation of the principles of the United Nations Charter, international law and the Statute of the Agency.”
The key words in this opinion are “devoted to peaceful purposes.” IAEA Director General Rafael Grossi has stated on multiple occasions, and the June 12 IAEA resolution reiterated, that the IAEA is not “in a position to provide assurance that Iran’s nuclear programme is exclusively peaceful.” Indeed, the IAEA has repeatedly publicized evidence that Iran’s nuclear facilities are not devoted to peaceful purposes. For example, Grossi has warned that the Iranian regime is now producing uranium enriched to a purity level which he says “only countries making bombs have” and noted the regime has amassed sufficient such “nuclear material for several nuclear weapons.”
It is also important to recognize that the nature of the threat Israel is addressing—both the imminent threat of Iran arming itself with a nuclear weapon and its existing ballistic missile capability focused on Israel—renders the scope of this campaign proportional as an act of self-defense. The Israeli military campaign appears to be aligned with the strategic objectives of disabling these threats. And it is difficult to imagine a self-defense objective more vital than eliminating the threat of being attacked with a nuclear weapon by a state that has already launched hundreds of ballistic missiles and drones into your territory and repeatedly threatened to destroy you. If assessed through the lens of self-defense, a military campaign focused on preventing Iran from achieving its objective of annihilating Israel—which in itself would be an international law violation of the gravest magnitude—is clearly proportional.
Israel is thus doubly justified in conducting a military campaign to rid itself and the world of an imminent threat that Iran’s leadership would acquire a nuclear weapon capable of achieving its objective of destroying Israel and its nine million inhabitants. During the ongoing Israel-Iran armed conflict, targeting the assets and personnel essential for weaponizing the nuclear material Iran has already accumulated is among the most compelling military objectives imaginable. And even if a self-defense justification were needed, the advanced state and purpose of Iran’s nuclear weapons program would provide sufficient basis.
The Iranian nuclear-capable missiles that struck Israeli cities last year (and again in recent days) underscore Iran’s determination to destroy Israel, its persistence in violating international law by targeting civilians, and the error of assuming Israel’s defenses would be sufficient to protect Israel from a nuclear attack and Iran’s missile arsenal. Israel, left with no choice but to take military action, had two strong legal rationales for doing so.
LTC Geoffrey Corn, USA (ret.), a Texas Tech University law professor and JINSA distinguished fellow, previously served as the U.S. Army’s senior law of war expert. Orde Kittrie, an Arizona State University law professor and senior fellow at the Foundation for Defense of Democracies, previously served as the lead U.S. State Department attorney for nuclear issues.
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