Strike first, argue later: The disputed legality of Israel’s Iran offensive

“We will take the initiative and attack the enemy… to assure the security of Israel and the future of the nation.” — Menachem Begin, defending Israel’s 1967 pre-emptive strike on Egypt.

Nearly six decades after Begin’s declaration, Israel has once again invoked that logic to justify its attack on Iran’s nuclear infrastructure. The framing is familiar: existential danger, pre-emptive action, national survival. But today, as in 1967, one fundamental question remains unresolved: was it legal?

Last month, Israel launched a bold and unprecedented air campaign deep inside Iranian territory. Over ten days, Israeli jets struck nuclear facilities, missile infrastructure, and senior military commanders. Israeli officials described the strikes as a “pre-emptive, precise… offensive,” intended to thwart what they called an “imminent existential threat”.

But the operation has sparked fierce debate. Under international law, specifically Article 2(4) of the UN Charter, the use of force against another state is prohibited, except when authorised by the Security Council or exercised in self-defence under Article 51. But what if the threat hasn’t yet materialised? Can a state legally strike first to prevent a future attack? As is often the case in international law, the answer is contested.

Many states in the Middle East, including UAE, Egypt and Saudi Arabia, condemned the strike as an illegal breach of Iranian sovereignty. Meanwhile, Western governments such as the United States, France and Germany cautiously affirmed Israel’s right to self-defence. The UN Security Council convened urgently but remained divided, highlighting the operation’s contested legal status.

This isn’t the first time Israel has launched a pre-emptive strike. In 1981, it bombed Iraq’s Osirak reactor; in 2007, it hit a Syrian facility. Both were surprise unilateral operations. The Osirak strike was unanimously condemned by the UN Security Council, while the Syria attack drew less formal censure, but was still seen as legally dubious.

Israel defends such actions under the Begin Doctrine, a national security principle that will prevent openly hostile regimes from going nuclear. For Israel, such strikes are a matter of survival, not theory. But under international law, the rule remains clear: military force is only lawful in response to an actual or imminent armed attack.

That’s what makes the 2025 strike so contentious. Israeli officials framed it as anticipatory self-defence, citing intelligence that Iran was just weeks away from achieving nuclear breakout. But critics argue it was simply a preventive unlawful offensive. Iran hadn’t launched a conventional attack. No missiles were fired from its territory, no jets scrambled.

Israel’s logic boiled down to this: act now or face a nuclear-armed Iran later.

That rationale echoes the so-called "Bush Doctrine", the US justification for its 2003 invasion of Iraq based on speculative “Weapons of Mass Destruction” threats. That war, and its legal basis, was widely criticised. The International Court of Justice (ICJ) has repeatedly rejected expanded readings of self-defence from the US in Nicaragua and a second case involving Uganda in the Democratic Republic of Congo.

The threshold remains high: force must respond to an actual or truly imminent attack. Anything less risks hollowing out the UN Charter’s core rule and setting a dangerous precedent.

Some Israeli legal scholars frame the situation differently: Israel and Iran, they argue, were already in an ongoing armed conflict. Iran has long backed groups like Hezbollah and Hamas, whose proxies launched repeated and deadly attacks on Israeli territory from 2023 onward. Iran itself fired missiles at Israel in 2024. From this perspective, the June 2025 strike wasn’t the start of a new war, it was an escalation in a conflict already underway.

Supporters of this view point to the ICJ’s Nicaragua judgment, which allows a state to defend itself not only against direct attacks, but also against a state that is heavily involved in attacks carried out by armed groups. If that logic applies, Israel’s strike might not need to be justified as a separate act of self-defence under the UN Charter. Instead, it would fall under the rules that govern how force is used once a conflict has already begun, a different and often more flexible legal framework.

Even when self-defence is permitted, international law imposes strict conditions: the force used must be necessary, proportionate, and in response to an imminent threat.

Israel argues it had no choice. Years of sanctions and diplomacy had failed. Iranian enrichment had crossed red lines and according to Israeli intelligence, Tehran was just weeks away from nuclear breakout. The strike, officials say, was a last resort, a move taken in a rapidly closing window.

Some scholars support this view, noting that the operation came just after the IAEA censured Iran and nuclear talks collapsed, developments that arguably strengthened Israel’s claim of necessity. But could Israel have waited for firmer evidence, or continued its sabotage campaign?  

Even if the threat was real, some argue the strike may not eliminate it, and could even accelerate Iran’s nuclear push. If the operation can’t stop the program, was it truly necessary?

This is perhaps the most contested legal issue. Israel’s defenders cite the 2012 Bethlehem Principles, which propose a broader reading of imminence, one that weighs the scale of potential harm, the nature of the threat (especially with nuclear weapons), and how little time remains to act.

But traditionalists push back. Under the classic Caroline formula (1837), anticipatory self-defence is only lawful when the threat is “instant, overwhelming, and leaving no choice of means”. It’s a deliberately high bar and many argue Israel did not meet it. They warn that lowering the threshold risks blurring legal boundaries and allowing states to label any future risk as “imminent”.

This test isn’t about matching firepower. It asks whether the scale and intensity of force used is excessive to the threat posed. Israel’s operation reportedly involved some 200 aircraft and multiple waves of strikes across Iranian territory. Analysts say it decapitated parts of Iran’s command structure and disrupted key nuclear infrastructure.

Supporters argue the scale was justified given the stakes: a potential nuclear-armed adversary. In ongoing armed conflicts, proportionality allows for some legal flexibility: states may use force not only to repel immediate threats but also to degrade an enemy’s capacity to strike again.

Critics see it differently. European legal scholar Marko Milanovic argues that occasional Hezbollah or Houthi rocket attacks can’t justify “bomb[ing] Iranian nuclear facilities, kill[ing] the whole military leadership, [and] attack[ing] many other targets”. On that view, Israel’s response wasn’t proportionate to the immediate threat, it was a sweeping campaign aimed at longer-term strategic advantage.

Israel’s recent strike on Iran sits at the uneasy intersection of existential fear and legal restraint. It sharpens a central dilemma: can a legal system built to limit state power adapt to a world of nuclear brinkmanship and proxy warfare? Or does the logic of survival now override the Charter’s carefully drawn red lines?

On paper, the law is clear. The UN Charter prohibits preventive war, no matter how grave the perceived threat. But law and geopolitics rarely align. Iran didn’t roll tanks across a border, but it did arm, fund, and direct proxies in a long-running shadow war. That ambiguity clouds legal assessments and lays bare the limits of a collective security system that too often watches from the sidelines.

In the end, Israel’s operation may not only test Iran’s nuclear ambitions, but it also tests whether the UN Charter is still fit for purpose in a region where the first strike might come with footnotes. International law may lack hard power, but it still shapes soft legitimacy.

For Israel, a state that trades on its law-abiding credentials, legal argument isn’t a postscript, it’s part of the battlefield. And for Western allies, whose backing depends not just on interests but on ideals, these legal debates are anything but academic.