For more than 100 days, U.S. warships have been stopping ships from entering or leaving Iran’s ports. The naval blockade is Washington’s main pressure tool in the Iran war: it aims to choke off Iran’s oil revenue without a full-scale invasion. Here is how the blockade works, what international law requires, and why it matters for oil prices and the chances of a deal.
Key takeaways
- The current blockade was reinstated on July 14, 2026, after an earlier one ran from April 13 to June 18.
- U.S. Central Command (CENTCOM) says it has blocked about $25 billion in Iranian crude exports and redirected 138 ships as of Oct. 17.
- Enforcement happens east of the Strait of Hormuz, in the Gulf of Oman and Arabian Sea — not in the strait itself.
- The blockade targets ships going to or from Iranian ports only; traffic to other Gulf states is not supposed to be blocked.
What is a naval blockade?
A blockade is a wartime operation that prevents ships of all nations from entering or leaving an enemy’s ports or coastline. It is different from sanctions, which are legal and financial restrictions, and different from a simple “quarantine” of certain cargoes. Because it affects neutral countries’ ships, a blockade is tightly regulated by the law of naval warfare.
What international law requires
Under widely cited rules such as the San Remo Manual and the U.S. Navy’s Commander’s Handbook (the “Newport Manual”), a lawful blockade must generally be:
- Declared and notified — with a start time, location, extent and a grace period for neutral ships already in port.
- Effective — backed by enough force that ships trying to run it are likely to be stopped.
- Impartial — applied equally to ships of all flags.
- Limited — it may not block access to neutral countries’ ports, and it must allow essential food and medical supplies when civilians lack them, subject to inspection.
Legal scholars continue to debate parts of the U.S. operation, including the legal basis for the wider war. As one analysis in Opinio Juris argued, CENTCOM’s decision to exempt ships traveling to non-Iranian ports is central to the blockade’s legality, because blocking access to neutral states such as Saudi Arabia, Qatar or Iraq would violate the rules.
How the blockade started
The war began with U.S. and Israeli strikes on Feb. 28, 2026. After U.S.–Iran talks in Islamabad collapsed on April 12, President Trump announced a blockade. CENTCOM’s order took effect the next day and limited enforcement to vessels entering or leaving Iranian ports and coastal areas. The blockade was lifted in June as part of the short-lived Islamabad Memorandum, then reinstated on July 14 when that deal broke down over transit rules and fees for the Strait of Hormuz.
How enforcement works at sea
U.S. forces — reported at more than 15,000 personnel, two carrier strike groups and over 200 aircraft and warships during the spring phase — patrol the approaches east of Hormuz. Ships suspected of heading to or from Iran can be hailed, boarded and searched. Depending on the situation, they can be redirected, disabled or seized. Humanitarian shipments are allowed after inspection.
Iran has relied on a “shadow fleet” of older tankers with obscured ownership to keep exporting oil. Industry trackers have disputed how airtight the blockade is at times, but intelligence firm Kpler reported in October that Iran’s shadow-fleet tankers had run out of oil to carry in mid-October.
Does the blockade close the Strait of Hormuz?
No — and that is a key point. The U.S. blockade targets Iranian trade. It is Iran’s own threats and attacks that have kept most commercial traffic out of the strait. Iran says it will reopen the waterway only if the U.S. lifts the blockade, eases oil restrictions, releases frozen assets and ends regional hostilities. Washington wants Iran’s nuclear program included in any deal. (Background: What is the Strait of Hormuz?)
Why it matters for Americans
- Oil and gas prices: Taking Iranian barrels off the market while Hormuz is disrupted keeps global supply tight.
- Risk of escalation: Boardings and strikes on blockade runners can trigger Iranian retaliation against shipping or Gulf states.
- Negotiating leverage: The blockade is a bargaining chip. Its future is tied to the debate over whether the U.S. strikes Iran again after the midterms.
Frequently asked questions
Is the U.S. blockading Iran right now?
Yes. CENTCOM marked 100 days of the reinstated blockade on Oct. 22, 2026.
Is a naval blockade an act of war?
Under international law, a blockade is a measure used during an armed conflict. The U.S. and Iran have been in open conflict since February 2026.
How many ships has the blockade stopped?
CENTCOM said the reinstated blockade had redirected 138 ships as of Oct. 17, 2026, and blocked about $25 billion in Iranian crude exports.
Information current as of late October 2026. This article is not legal advice.
