Völkerrechtswidrig: What International Law Actually Says About the Iran War

German President Frank-Walter Steinmeier called the war against Iran a violation of international law on March 24, 2026. Speaking at the 75th anniversary of the reconstitution of the German Foreign Office, he stated: "This war is a breach of international law - there is little doubt about that." He called it "a politically disastrous mistake" and "a truly avoidable, unnecessary war, if its goal was to stop Iran on the path to the atomic bomb." These are not vague expressions of disapproval. They are legal assessments from a former foreign minister who spent years negotiating the Iran nuclear deal. The question this article addresses: does the assessment hold under existing international law? What follows is the legal framework, the competing arguments, and the precedents. The reader will judge.

What Steinmeier Actually Said

Steinmeier used the term "Völkerrechtsbruch" (breach of international law) to describe the US-led military strikes against Iran. He specified that there was "little doubt" that "at least the justification with an immediately imminent attack on the USA does not hold up." CDU/CSU foreign policy spokesman Jürgen Hardt responded that the German government, "which is solely responsible for this question, has not yet completed its legal review." Chancellor Friedrich Merz distanced himself from the war but, unlike some European partners, stopped short of declaring the strikes a violation of international law. The AfD agreed with Steinmeier's characterization. The political reaction matters, but the legal question stands on its own.

The Prohibition of Force: Article 2(4)

The starting point for any legal assessment is Article 2(4) of the United Nations Charter. The provision states that all member states "shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state." This is the bedrock principle of the post-1945 international order. It represents a fundamental departure from the pre-war system in which states held a general right to wage war.

The Charter permits two primary exceptions to this prohibition. First, the Security Council may authorize the use of force under Chapter VII when it determines the existence of a threat to international peace and security. Second, Article 51 preserves the "inherent right of individual or collective self-defense if an armed attack occurs."

No Security Council resolution authorized the US-Israeli military strikes against Iran that began on February 28, 2026. The Security Council did adopt Resolution 2817 (2026) by a vote of 13 in favor to none against, with Russia and China abstaining, but that resolution condemned Iran's retaliatory attacks on neighboring Gulf states. It did not authorize the initial US-Israeli strikes. A separate Russian-drafted resolution calling on all parties to immediately cease military activities was rejected by a vote of 4 in favor to 2 against (Latvia and the United States), with 9 abstentions.

Without Security Council authorization for the initial strikes, the legal burden rests entirely on the self-defense argument under Article 51.

The Self-Defense Argument: Article 51

The United States and Israel both publicly invoked self-defense to justify the strikes. On February 28, 2026, President Trump released a video statement citing Iran's "menacing activities," including its nuclear program, support for proxy forces such as Hamas and Hezbollah, the Iran hostage crisis, and attacks on protesters. Prime Minister Netanyahu emphasized the existential nature of the Iranian nuclear threat and sustained attacks by Iran-backed militias.

The factual basis included IAEA reports confirming that Iran had accumulated approximately 440.9 kilograms of uranium enriched to 60 percent of the U-235 isotope as of the agency's September 2025 verification report. While 60 percent is well beyond any plausible civilian use, it is not weapons-grade. Weapons-grade uranium requires enrichment to approximately 90 percent. However, the technical step from 60 to 90 percent requires only about 1 percent of the separative work already invested, meaning Iran's breakout capability was measured in weeks rather than months. Iran had also significantly expanded its ballistic missile program and maintained active proxy forces in Lebanon, Syria, Iraq, and Yemen. In October 2025, Iran officially withdrew from the JCPOA, declaring all restrictions on its nuclear program void.

These facts provide context. The legal question is whether they constitute an "armed attack" within the meaning of Article 51, and whether the strikes, which killed Supreme Leader Ali Khamenei and targeted nuclear and military infrastructure, constituted a lawful response.

The Anticipatory Self-Defense Debate

This is the central legal battleground. Article 51 refers to self-defense "if an armed attack occurs." The plain text suggests a reactive right: a state may defend itself after being attacked. The US and Israeli argument requires a broader reading, one that includes the right to act before an attack materializes.

International law has long recognized a limited concept of anticipatory self-defense. The foundational reference point is the Caroline incident of 1837, in which British forces destroyed an American vessel supplying Canadian rebels. US Secretary of State Daniel Webster established the criteria that self-defense requires a "necessity of self-defense, instant, overwhelming, leaving no choice of means, and no moment for deliberation."

The International Court of Justice addressed self-defense in several landmark cases. In Nicaragua v. United States (1986), the Court rejected Washington's claim that its support for the Contras constituted collective self-defense. The ruling established a high threshold for what constitutes an armed attack, distinguishing it from lesser uses of force. In the Oil Platforms case (2003), brought by Iran against the United States, the Court found that US attacks on Iranian oil platforms in 1987-1988 did not meet the necessity and proportionality requirements of self-defense. In Armed Activities on the Territory of the Congo (2005), the Court again applied a restrictive interpretation.

A critical distinction runs through this jurisprudence: anticipatory self-defense (responding to an imminent attack) versus preventive self-defense (acting against a future, non-imminent threat). The former finds some support in customary international law under the Caroline criteria. The latter does not.

The Bush Doctrine, articulated in the 2002 National Security Strategy, attempted to expand the self-defense concept to encompass preventive military action against states developing weapons of mass destruction. This doctrinal expansion was widely rejected by the international legal community at the time.

The Iran case falls uncomfortably between these categories. Iran had not launched a direct military attack on the United States or Israel at the time the February 28 strikes occurred. UN Special Rapporteur on counterterrorism Ben Saul stated that "this is not lawful self-defence against an armed attack by Iran, and the UN Security Council has not authorised it." Marko Milanovic, professor of public international law at the University of Reading, argued on EJIL:Talk! that even under the broadest anticipatory self-defense theory, three conditions must be met: Iran's leadership decided to attack, Iran possessed the capability, and force was necessary at that moment as the last opportunity to prevent the attack. In his assessment, "none of these conditions are met here."

The counter-argument draws on the concept of an ongoing armed conflict. Maj. Gen. Charles Dunlap (ret.), a Duke Law professor, argued that the US was already in an established armed conflict with Iran spanning decades of proxy attacks on US personnel and assets. Under this theory, once a state has lawfully resorted to force in self-defense following an armed attack, "it is not necessary to reassess whether an armed attack is imminent prior to every subsequent action" provided hostilities continue. Dunlap also cited the "last feasible window of opportunity" standard, arguing that Iran's proximity to nuclear capability created a closing window for action. This argument has intellectual force but rests on a contested expansion of existing doctrine.

Iran's Retaliatory Strikes and Their Legal Consequences

The legal picture became significantly more complex after February 28. Iran responded to the US-Israeli strikes with missile and drone attacks targeting Israel, US military bases in the region, and the territory of Gulf states hosting US assets. Iranian strikes hit targets in Bahrain, Kuwait, Qatar, the UAE, Oman, and Jordan, killing civilians and military personnel in countries that had not participated in the initial strikes.

This retaliation created a layered legal problem. While Iran could potentially invoke self-defense against the states that attacked it, its strikes against Gulf states that had not allowed their territory to be used for the initial aggression raised serious legal questions. Legal analysts at Just Security argued that Iran cannot lawfully strike US bases in Gulf states if those countries "had not allowed their territory to be used" for aggression against Iran. The same analysts noted Iran's own precedent: in a 1993 ICJ argument, Iran itself contended that attacks on distant bases are "illegitimate because directed at the wrong target."

The UN Security Council's Resolution 2817 condemned precisely these Iranian strikes against Gulf neighbors, passing with 135 co-sponsoring states. This resolution does not address the legality of the initial US-Israeli strikes. The legal assessments of the two phases of the conflict operate independently.

The Precedents: Kosovo, Iraq, Libya

Three modern military interventions illuminate the legal terrain.

NATO's bombing of Yugoslavia in 1999 to stop the Kosovo crisis proceeded without Security Council authorization. NATO chose not to seek a resolution, knowing Russia and China would veto. After bombing began, a Russian-Indian-Belarusian draft resolution demanding cessation of force was rejected by a vote of 3 in favor to 12 against on March 26, 1999. The Independent International Commission on Kosovo, established afterward, concluded that the intervention was "illegal but legitimate." This formulation acknowledged the violation of the Charter framework while arguing a moral case. It created no legal precedent.

The 2003 Iraq War offers a parallel to the Iran case. The US and UK cited UN Security Council Resolutions 678 (1990) and 687 (1991) as providing continuing authorization for the use of force. The legal community overwhelmingly rejected this argument. UN Secretary-General Kofi Annan stated in September 2004 that the invasion was "not in conformity with the UN Charter" and was "illegal." The Chilcot Inquiry in the UK (published July 6, 2016) concluded that "the circumstances in which it was decided that there was a legal basis for UK military action were far from satisfactory."

The Libya intervention of 2011 followed a different path. Security Council Resolution 1973 authorized "all necessary measures" to protect Libyan civilians. NATO interpreted this mandate as permitting the overthrow of the Gaddafi government. Russia and China, which had abstained rather than vetoed Resolution 1973, accused NATO of exceeding the authorized mandate. The Libya experience poisoned subsequent Security Council cooperation, contributing directly to the paralysis over Syria and, later, Iran.

None of these precedents established a legal basis for unilateral military action without Security Council authorization or a clear armed-attack trigger for Article 51.

What Legal Scholars Say

The international law community has produced rapid analysis of the Iran strikes. The weight of published scholarship tilts against the legality of the initial US-Israeli action.

Marko Milanovic, professor of public international law at the University of Reading, published an analysis on EJIL:Talk! titled "The American-Israeli Strikes on Iran are (Again) Manifestly Illegal," arguing that the strikes constitute "a plain violation of the prohibition on the use of force in Article 2(4) of the UN Charter."

Rebecca Ingber, professor at the Cardozo School of Law, emphasized to Al Jazeera that states "may not use force against the territorial integrity of other states except in two narrow circumstances - when authorised by the UN Security Council or in self-defence against an armed attack."

Yusra Suedi, at the University of Manchester, argued that the imminence threshold was not met, noting that "imminence in international law is really understood to be something that is instant, something that is overwhelming, something that leaves really no other choice but to act first."

Claus Kreß, professor at the University of Cologne and Special Adviser to the ICC Prosecutor on the Crime of Aggression, has noted that the strikes raise serious questions under the definition of aggression adopted by the ICC Assembly of States Parties. The use of armed force against a state without Security Council authorization and without a clear armed-attack trigger fits the general definition of aggression under Resolution 3314.

On the other side, Maj. Gen. Charles Dunlap (ret.) at Duke Law offered three independent justifications: ongoing armed conflict, the evolved concept of imminence as a "last feasible window of opportunity," and humanitarian intervention based on Iran's violent crackdown on domestic protests. The humanitarian intervention argument draws on the Kosovo precedent of "illegal but legitimate" but, as Dunlap himself acknowledged, lacks explicit legal authority absent UN authorization.

The legal debate is not evenly split. Published assessments from international law scholars overwhelmingly find the legal justification for the initial strikes insufficient. The self-defense argument faces high doctrinal hurdles under the ICJ's established jurisprudence.

Proportionality and Jus in Bello

Even if the initial decision to use force (jus ad bellum) were legally defensible, the conduct of military operations must meet separate requirements under international humanitarian law (jus in bello). The principles of distinction, proportionality, and precaution apply regardless of whether the war itself is legal.

The ICRC president stated that the military escalation "is igniting a dangerous chain reaction across the region, with potentially devastating consequences for civilians" and that "upholding the rules of war is an obligation and not a choice." Reports indicate significant civilian casualties from strikes by both sides. Al Jazeera reported that US-Israeli strikes killed over one hundred civilians including children in a school. Iranian retaliatory strikes against Gulf states killed and injured civilians in Bahrain, Kuwait, Qatar, and other countries.

Both sides face jus in bello scrutiny. The targeting of dual-use infrastructure, including nuclear facilities, power systems, and transportation networks, raises questions under the principle of distinction between military and civilian objects. The proportionality requirement prohibits attacks where the expected civilian harm is excessive in relation to the concrete and direct military advantage anticipated.

The ICC Question

The International Criminal Court has jurisdiction over the crime of aggression, defined in amendments to the Rome Statute adopted at the Kampala Review Conference in 2010 and activated in 2018. The crime of aggression covers the "planning, preparation, initiation or execution" of an act of aggression that constitutes a "manifest violation of the Charter of the United Nations."

However, the ICC's aggression jurisdiction faces severe constraints. Neither the United States, Israel, nor Iran is a party to the Rome Statute. The ICC could exercise jurisdiction only through a Security Council referral under Chapter VII, which is politically implausible given the current Council dynamics.

Iran's Red Crescent has urged the ICC to examine alleged strikes on civilian sites as possible war crimes. Iranian opposition groups have separately filed a communication requesting a preliminary examination under Article 15 of the Rome Statute into alleged crimes against humanity by the Iranian regime during protest crackdowns. The ICC Prosecutor's office has not announced a formal investigation into either dimension of the conflict as of late March 2026.

An alternative accountability pathway exists through the International Court of Justice. The South Africa v. Israel case on the application of the Genocide Convention, filed in December 2023, demonstrated that ICJ proceedings can advance even without the respondent state's full cooperation, though enforcement of ICJ rulings depends on Security Council action.

Realistically, international legal accountability for the use of force remains constrained by the same power dynamics that shape the Security Council itself.

What We Know, What We Do Not Know, What Circulates Falsely

What we know. No UN Security Council resolution authorized the initial US-Israeli strikes against Iran. The US and Israel publicly invoked self-defense. The IAEA confirmed Iranian enrichment to 60 percent, with breakout capability to weapons-grade measured in weeks. Iran retaliated by striking Gulf states, US bases, and Israel, leading to UNSC Resolution 2817 condemning those attacks. The ICJ has consistently applied a restrictive interpretation of Article 51 in its case law. The majority of published international law scholarship considers the legal basis for the initial strikes insufficient under current frameworks.

What we do not know. Whether the US and Israel filed formal Article 51 notification letters, and their full content, has not been publicly confirmed. Whether back-channel negotiations were active at the time strikes commenced remains disputed. The complete scope of military operations, targeting decisions, and civilian casualties on all sides is not yet documented in independent assessments. Whether the ICC Prosecutor is conducting preliminary examinations has not been confirmed or denied.

What circulates falsely. Claims that NATO collectively authorized or endorsed the strikes are false. NATO as an organization did not invoke Article 5, though it prepared for possible activation after an Iranian missile entered Turkish airspace. Individual NATO members made bilateral decisions. Claims that the IAEA endorsed or supported military action are also false. The IAEA confirmed damage to the Natanz facility from satellite imagery but took no position on the legality or advisability of strikes. Its mandate is technical monitoring, not security policy. Claims that Iran enriched uranium to 90 percent (weapons-grade) before the war are false. Iran's highest confirmed enrichment level was 60 percent. The distinction matters: 60 percent is not weapons-grade, though the remaining technical step is small.

The predominant weight of international law, as interpreted by the ICJ and the majority of published scholarship, holds that military action against a state requires either Security Council authorization or a response to an actual or clearly imminent armed attack. The US-Israeli case for the initial Iran strikes rests on an expanded reading of self-defense that lacks firm support in existing jurisprudence. Steinmeier's assessment that the war is "völkerrechtswidrig" aligns with the mainstream of international legal scholarship, though the legal picture is complicated by Iran's subsequent retaliatory strikes against uninvolved Gulf states, which themselves violated international law. The legal verdicts on the two phases of this conflict operate independently, and both raise serious questions.