What Happened
- Iran closed the Strait of Hormuz again on April 18, 2026, one day after declaring it open, accusing the United States of violating a prior understanding by maintaining a naval blockade of Iranian ports.
- The Islamic Revolutionary Guard Corps (IRGC) warned that any vessel approaching the Strait of Hormuz would be considered as cooperating with the enemy and would be targeted.
- Two Indian-flagged ships, including the VLCC Sanmar Herald, were fired upon by Iranian gunboats while attempting to transit the strait, highlighting the direct risk to neutral commercial shipping.
- Iran's position was that the Strait would remain under IRGC control for as long as the US blockade of Iranian ports remained in force.
- The US Naval blockade, announced on April 13 and operating under US Central Command, targeted only vessels travelling to and from Iranian ports, while claiming non-interference with general freedom of navigation.
Static Topic Bridges
The Strait of Hormuz — Strategic Chokepoint
The Strait of Hormuz is a narrow waterway connecting the Persian Gulf to the Gulf of Oman and the Arabian Sea, with a width of approximately 21 nautical miles at its narrowest point. It is flanked by Iranian territory on the north and Oman on the south. The strait is the world's single most critical maritime chokepoint for energy trade.
- Approximately 20–25% of the world's seaborne oil trade and 20% of global LNG supplies pass through the strait annually.
- By 2025, roughly 15 million barrels of oil per day transited the strait.
- Daily traffic ranges from 80 to 130 ships; over 30,000 tankers transit annually.
- Neither Iran nor the United States has ratified UNCLOS (UN Convention on the Law of the Sea), though both invoke its provisions selectively.
Connection to this news: Iran's leverage over global energy markets stems directly from its geographic control over the strait. Any closure — even a partial or contested one — raises oil prices sharply and disrupts supply chains worldwide.
Transit Passage Rights Under UNCLOS
The United Nations Convention on the Law of the Sea (UNCLOS), adopted in 1982 and in force since 1994, establishes the legal framework for maritime navigation. Under Part III, Articles 37–44, all ships and aircraft enjoy the right of "transit passage" through straits used for international navigation, and this right cannot be suspended by coastal states. The framework was created as a compromise: coastal states gained the right to extend territorial waters to 12 nautical miles, but in exchange, they had to accept unimpeded transit through international straits.
- Iran enacted its own maritime law in 1993 that conflicts with UNCLOS — requiring warships and nuclear-powered vessels to obtain prior permission before exercising innocent passage.
- Iran's position is that any foreign military activity in the strait during active hostilities constitutes hostile action.
- International legal scholars are divided on whether a wartime naval blockade targeting only one state's ports constitutes a lawful belligerent act or an unlawful interference with freedom of navigation.
Connection to this news: Iran invokes its own maritime law and the context of active armed conflict to justify closing the strait, while the US frames its port-specific blockade as consistent with international law. The divergence has no clear arbiter in a conflict situation.
US Naval Blockade — Law of Naval Warfare
A naval blockade is a recognized act of war under the law of naval warfare, distinct from peacetime maritime law. Under customary international law and the 1909 Declaration of London, a lawful blockade must be declared, effective, and applied impartially to all neutral parties — it cannot single out one nation's shipping without broader declaration. The US announced on April 13, 2026, that it would blockade Iranian ports specifically, directing ships to turn back to Iran, with 21 ships already turned back.
- The US framed the blockade as applying only to ships travelling to or from Iranian ports, not as a closure of the strait itself.
- Critics argued the port-specific blockade still constituted an act of economic warfare against a third country without UN Security Council authorization.
- Iran's counter-move — reimposing strait controls — essentially matched a blockade with a blockade, creating a standoff with global economic consequences.
Connection to this news: The legitimacy of the US blockade is central to Iran's justification for reimposing strait restrictions. Iran frames its action as a response to an unlawful blockade, not as an aggressive act.
Key Facts & Data
- The Strait of Hormuz was first closed by Iran in the early days of the 2026 Iran-Israel-US war, which began on February 28, 2026.
- The US naval blockade was announced on April 13, 2026, following the collapse of the Islamabad Talks.
- Iran declared the strait "completely open" briefly before reimposing control on April 18.
- 21 ships were turned back to Iran by US forces within the first days of the blockade.
- Two Indian-flagged vessels came under gunfire in the strait following reimposition of Iranian controls.
- Global oil prices have been sharply elevated since the start of the 2026 conflict.