U.S. strikes Iran for third day, will reimpose blockade
The US military carried out a third consecutive day of strikes on Iranian targets, with reports indicating that a negotiated deal with Iran was still considered possible even as the strikes continued
The US administration announced the reimposition of a naval blockade on Iranian ports and shipping
Iran struck two tankers transiting the Strait of Hormuz, killing one crew member, in what was described as retaliation
The escalation followed the collapse of a truce period established after an earlier memorandum of understanding between the two countries
UN Charter Article 2(4) and Article 51 — Prohibition and Exception on Use of Force
Article 2(4) of the UN Charter is the foundational prohibition on the use of force in international relations, requiring all member states to refrain from the "threat or use of force against the territorial integrity or political independence of any state." Article 51 preserves one of only two recognised exceptions to this prohibition: the "inherent right of individual or collective self-defence if an armed attack occurs" against a UN member.
Key Details
- The two accepted exceptions to Article 2(4) are: (i) self-defence under Article 51, and (ii) UNSC-authorised enforcement action under Chapter VII
- Self-defence under Article 51 is available only "until the Security Council has taken measures necessary to maintain international peace and security"
- States exercising Article 51 self-defence must "immediately report" the measures taken to the Security Council
- Customary international law requires such action to be necessary and proportionate — principles traced to the 1837 Caroline case
Continued US strikes on Iranian targets and Iran's retaliatory strikes on shipping are both being framed in self-defence terms by the respective sides, placing the exchange squarely within the Article 2(4)/Article 51 framework that governs the legality of inter-state force.
Naval Blockade Under International Law — the San Remo Manual
A naval blockade is a method of warfare aimed at preventing vessels from entering or leaving specified ports or coastlines. Its legality is governed by customary international law as codified in the 1994 San Remo Manual on International Law Applicable to Armed Conflicts at Sea, drafted under the International Institute of Humanitarian Law.
Key Details
- A lawful blockade must be declared and notified to all belligerents and neutral states, specifying its commencement, duration, location and extent
- It must be effective — a blockade that is not actually enforced is not legally valid
- It must not bar humanitarian passage: if a blockaded population is inadequately supplied with essential goods, the blockading power must allow free passage of such supplies
- The San Remo Manual is not itself a binding treaty but is treated as an authoritative restatement of customary law integrating the 1949 Geneva Conventions framework for naval warfare
The reimposition of a blockade on Iranian shipping raises the same legal tests — declaration, effectiveness and humanitarian exception — that determine whether such a blockade is a lawful method of warfare or an unlawful act of force against neutral commerce.
UNCLOS Transit Passage Through International Straits
The Strait of Hormuz is classified as a strait used for international navigation under the UN Convention on the Law of the Sea (UNCLOS, 1982), which grants all ships and aircraft the right of "transit passage" — a right that formalised earlier customary law recognised in the Corfu Channel case (ICJ, 1949).
Key Details
- Article 38 of UNCLOS defines transit passage as the exercise of freedom of navigation and overflight solely for continuous and expeditious transit between one part of the high seas/EEZ and another
- The right applies to all ships and aircraft, military and civilian alike, and cannot be impeded by the bordering states
- Article 44 of UNCLOS specifically provides that transit passage "shall not be suspended," even during heightened tensions
- UNCLOS entered into force in 1994; Iran has signed but not ratified UNCLOS, while the US has neither signed nor ratified it, complicating enforcement of these provisions in the current crisis
Both the US blockade and Iranian strikes on tankers effectively interrupt transit passage through the Strait of Hormuz — passage that UNCLOS Article 44 says may not be suspended even in situations of tension, underscoring the tension between the legal framework and the on-ground military reality.
- UN Charter Article 2(4): general prohibition on the threat or use of force between states
- UN Charter Article 51: self-defence exception, subject to necessity, proportionality and mandatory reporting to the UNSC
- San Remo Manual (1994): governing customary-law restatement for lawful naval blockades — requires declaration, effectiveness, and humanitarian passage
- UNCLOS Article 38: right of transit passage for all vessels through straits used for international navigation
- UNCLOS Article 44: transit passage through such straits "shall not be suspended"
- UNCLOS entered into force in 1994; neither Iran nor the US has ratified it