International humanitarian law — the body of rules that governs how wars are conducted — does not prohibit war itself. It prohibits specific conduct within war. The distinction matters enormously for assessing what has happened in the first 24 days of the US-Israel conflict with Iran.
The question is not whether terrible things have happened. They have. Iranian missiles have struck towns near Israel's Dimona nuclear facility, injuring 180 people. US-Israeli strikes have hit residential buildings in Urmia and Tabriz. Iran has struck desalination and energy infrastructure across the Gulf. Schools and hospitals have been hit. More than 1,500 people have been killed in Iran; over 1,000 in Lebanon.
The legal question is different: under the rules that all three parties are bound by, which of these acts constitute violations — and which fall within the permissible conduct of armed conflict, however devastating that conduct may be?
The Legal Framework: What Actually Applies
International humanitarian law (IHL) — also known as the laws of armed conflict or the law of war — is primarily codified in the four Geneva Conventions of 1949 and their Additional Protocols of 1977. All three parties (the US, Israel, and Iran) are parties to the Geneva Conventions. The key rules relevant to the current conflict:
Distinction: Parties must distinguish between civilians and combatants, and between civilian objects and military objectives. Only military objectives may be deliberately attacked. A military objective is defined as "objects which by their nature, location, purpose or use make an effective contribution to military action and whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military advantage."
Proportionality: Even when attacking a legitimate military objective, an attack is prohibited if it causes incidental civilian casualties that are "excessive in relation to the concrete and direct military advantage anticipated." Proportionality requires a genuine case-by-case military judgment — it does not prohibit civilian harm, only "excessive" civilian harm.
Precaution: Parties must take all feasible precautions to avoid civilian casualties, including verifying targets are military objectives, choosing means and methods that minimize civilian harm, and giving advance warning when civilians can be evacuated without compromising the mission.
Protection of specific objects: Hospitals, clearly marked medical facilities, schools (when not used for military purposes), and objects "indispensable to the survival of the civilian population" (including food, water, and energy essential for civilian survival) have heightened protection.
Prohibited weapons: Cluster munitions (under the Convention on Cluster Munitions), chemical weapons (Chemical Weapons Convention), and indiscriminate weapons — those that cannot be directed at a specific military target — are prohibited regardless of target.
The US-Israel Position: Self-Defense and Military Necessity
The US legal justification for the war, articulated by the administration, rests on Article 51 of the UN Charter: the right of self-defense. The administration has cited Iran's nuclear program as an existential threat and Iran's support for attacks on Israel (through Hezbollah, Hamas, and direct missile strikes) as the predicate for the defensive use of force.
Former US State Department legal adviser Brian Finucane, now at the International Crisis Group, has been among the most prominent critics of the legal basis. The core challenge to the Article 51 justification: Article 51 permits self-defense "if an armed attack occurs." The lawfulness of preventive self-defense — striking a country to prevent a future attack it hasn't yet launched — is contested in international law. The US has argued for a broad "anticipatory self-defense" doctrine since at least the 2002 Bush National Security Strategy; most international lawyers regard this doctrine as incompatible with the UN Charter's text.
On targeting: US and Israeli strikes have hit IRGC headquarters, missile production facilities, military bases, and command infrastructure — all potentially legitimate military objectives under IHL. The harder cases are strikes on residential buildings in Tabriz, Urmia, and other Iranian cities where civilian casualties are confirmed. The legal defense available is dual-use: if a residential building was being used for military purposes (weapons storage, command node), it becomes a military objective. Whether the US-Israeli targeting intelligence actually supported those determinations cannot be independently verified.
The threatened strikes on Iranian power plants — the subject of Trump's 48-hour ultimatum — raise the sharpest legal questions. Power plants are civilian infrastructure and are afforded protection under Additional Protocol I, Article 54 (objects indispensable to civilian survival). An exception applies if the infrastructure is used "in direct support of military action" — but power plants serving entire civilian populations cannot be characterized that way without significant legal strain.
Iran's Position: Response to Unlawful Aggression
Iran's legal framing is the inverse: it characterizes the US-Israeli strikes as unlawful aggression under the UN Charter, and its own actions as lawful self-defense under Article 51. This framing has some international support — the US intelligence assessment (per Director Gabbard's March 18 statement) that Iran was "not on the verge of making nuclear bombs" undermines the US preventive self-defense justification.
Iran's missile strikes on Israeli territory — including the strikes near Dimona that injured 180 people — present their own legal questions. If directed at military targets (Israel's nuclear facility is a dual-use site with significant military dimensions), they could be characterized as lawful military strikes. If intended to strike civilian population centers or indiscriminate in their effects, they would violate the distinction principle.
Iran's threats to strike desalination and power infrastructure in Gulf states hosting US bases are the clearest potential IHL violations from the Iranian side. Desalination plants are explicitly protected under Additional Protocol I as objects indispensable to civilian survival. A deliberate strike on a desalination plant serving a civilian population would be a serious violation of IHL regardless of the military justification offered — there is no "dual-use" argument available for a facility whose sole purpose is producing civilian drinking water.
Iran's strikes on Gulf state infrastructure — Saudi Arabia, UAE — targeting US military bases introduce an additional complication: these are attacks on neutral or allied third states. Unless Saudi Arabia and UAE are considered co-belligerents (which they may be, given they are hosting US forces), Iran's strikes on their territory require a separate legal justification.
The Hospital and School Strikes
Geoffrey Nice KC — the former ICC prosecutor who led the case against Slobodan Milošević — has noted that strikes on medical facilities and schools carry a higher burden for the attacking party. Under the Geneva Conventions, medical facilities lose their protection only if they are "used to commit acts harmful to the enemy" — and even then, only after a warning is given and not heeded.
Documentation of hospital and school strikes in Iran, Lebanon, Gaza, and the West Bank has been extensive. Human Rights Watch, Amnesty International, and UN agencies have published reports on specific incidents. The legal standard requires demonstrating either that the facility was being used for military purposes at the time of the strike, or that the strike was targeting something nearby and the hospital was collateral damage within proportionality limits.
Nice's concern, consistent with his ICC experience, is about the pattern of such strikes: when medical facilities and schools are hit repeatedly by the same party across multiple conflicts, the legal defense of individual targeting decisions becomes less credible. Pattern evidence was significant in the Milošević prosecution.
The Hormuz Blockade: A Different Body of Law
Iran's effective closure of the Strait of Hormuz implicates a body of law distinct from IHL: the UN Convention on the Law of the Sea (UNCLOS) and the customary international law of naval warfare.
The Strait of Hormuz is an international strait — defined under UNCLOS as a body of water used for international navigation connecting two parts of the high seas. Under UNCLOS Article 38, all states enjoy the right of "transit passage" through international straits, which cannot be suspended. Blocking transit passage through an international strait is a violation of UNCLOS.
The US is not a party to UNCLOS (the Senate has never ratified it), but accepts most of its provisions as customary international law. Iran is a party. Iran's closure of Hormuz shipping lanes is therefore, in the view of the US, UK, and most international lawyers, a violation of its UNCLOS obligations.
Iran's counter-argument is that its actions are justified by the UN Charter right of self-defense — that closing Hormuz to shipping is a defensive military measure against states that are attacking it. This argument has some support in the law of naval warfare, which permits belligerents to establish exclusion zones, but it is contested whether an exclusion zone can lawfully encompass an international strait.
Who Can Actually Enforce Any of This?
International law's fundamental limitation is enforcement. The mechanisms that exist:
UN Security Council: The primary enforcement mechanism under the UN Charter. Blocked. The US has veto power and has used it repeatedly to block resolutions critical of US or Israeli actions. Russia and China have vetoed resolutions critical of Iran. The Security Council is effectively paralyzed on this conflict.
International Criminal Court: The ICC has jurisdiction over war crimes committed by nationals of member states or on the territory of member states. Israel is not a party to the Rome Statute. The US is not a party. Both have explicitly opposed ICC jurisdiction over their nationals. Iran is a party to the Rome Statute, which means ICC could theoretically investigate Iranian nationals for crimes committed in the conflict. However, the ICC prosecutor would need to open an investigation, which requires resources and political will that typically takes years to materialize.
International Court of Justice: The UN's primary judicial body can hear cases between states. Iran has previously filed ICJ cases against the US (the 1980 hostage crisis case, which the US eventually settled). Multiple states could theoretically file ICJ cases alleging violations. ICJ proceedings take years and produce declaratory judgments that require Security Council enforcement — also blocked.
Universal jurisdiction: Some states exercise criminal jurisdiction over war crimes regardless of where they were committed. Spain, Germany, and Belgium have historically exercised universal jurisdiction. Third-state prosecutions of senior US, Israeli, or Iranian officials are theoretically possible but practically unlikely given the political implications.
Professor Nicholas Tsagourias of Sheffield notes the structural reality: "International law exists and applies. Accountability requires political will. Political will requires geopolitical conditions that currently don't exist for any of the three parties in this conflict."
The Accountability Gap — And Why It Matters Anyway
The absence of near-term enforcement doesn't make the legal assessment irrelevant. It matters for several reasons:
Future accountability: The Nuremberg trials happened four years after the conduct they prosecuted. Milošević was indicted seven years after Srebrenica. The ICC indictment of Putin (for the deportation of Ukrainian children) came a year into the Ukraine war. Legal accountability operates on longer timelines than military and diplomatic events.
Third-state behavior: International law constrains what neutral states can do — supplying weapons to a party committing war crimes creates legal risk for the supplier. Germany's early pause on arms transfers to Israel in 2023-2024 reflected this concern. The legal picture affects the political feasibility of arms transfers and financial transactions.
Post-conflict settlement: Peace agreements typically require some accountability mechanism. The legal characterization of conduct during the war shapes what a post-conflict justice process can include.
Whether international law has been violated in the Iran war depends on factual determinations — specific targeting decisions, specific intelligence assessments, specific proportionality calculations — that the parties themselves control and the international community cannot independently verify in real time. The law is clear. The facts are contested. That gap is where wars are fought and where accountability is lost.