US Navy sea blockade on Iran intensifies Strait of Hormuz shipping and energy supply risks

The US Navy has begun a sea blockade against Iran, raising tensions in a conflict that has already cut energy flows through the Strait of Hormuz. Adm Brad Cooper said on Wednesday that the action started on Monday and was now fully in place. Cooper said US forces had stopped sea trade in and out of Iran.

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Central Command said it was applying the blockade to any vessel entering or leaving Iranian ports. It said ships not heading to Iranian ports still had freedom of navigation. In the first 48 hours, it said no ship passed US naval forces while trying to access Iran. It said nine vessels turned back after US orders.

US naval blockade against Iran: How enforcement is working

A US official told The Associated Press that US forces are operating in the Gulf of Oman beyond the Strait. The plan is to watch ships leave Iranian facilities and clear the Strait of Hormuz. US forces then intercept and order those vessels to return. The official spoke anonymously due to operational sensitivity.

The official said the military uses more than AIS tracking beacons to confirm port origin. The official did not offer more detail, citing the need for operational security. A notice to mariners said enforcement is in the Gulf of Oman and Arabian Sea. That means crossing the Strait alone does not confirm a ship avoided the blockade.

The terms also included a grace period for departures from Iran until 1400 GMT on Monday. Humanitarian cargo, including food and medical supplies, will be allowed subject to inspections. A legal guide cited by Sal Mercogliano said naval law permits blockades. It also bars blockades aimed only at starving civilians.

US naval blockade against Iran: Shipping data shows disruption

Shipping data firms reported that Iran-linked or sanctioned ships left the Gulf through the Strait. Many then stopped or reversed course, amid location jamming and spoofing risks. Ana Subasic of Kpler said only eight vessels transited on Tuesday. Most were linked to Iran or sanctions. Subasic said the operating environment remained extremely high risk.

Subasic said several ships reduced movement after clearing the Strait. Subasic said that suggested early effects from the blockade. Many of those vessels had carried Iranian-origin sanctioned cargo. Subasic said the Rich Starry tanker, carrying methanol, left the Gulf. The ship later halted, made a U-turn, and went back through the Strait.

Windward said vessel patterns showed an uneven reaction to the blockade. It said sanctioned and false-flagged ships stayed active, with mixed decisions. Some sailed through the Strait, while others delayed or turned around. Analysts also noted ships can send false AIS positions or switch off AIS. That adds to uncertainty for shipowners.

US naval blockade against Iran: Strait of Hormuz impact and oil flows

Iran previously choked the Strait by threatening attacks on shipping. That cut about 20% of the world’s daily oil consumption. Oil prices rose sharply, with warnings of inflation and recessions in major economies. Ships were struck by aerial and undersea drones and unknown projectiles, killing 11 crew members. While attacks have fallen, traffic is down over 90%.

Some oil is still leaving through pipelines to the Red Sea and Gulf of Oman. However, those routes cannot replace the Strait’s capacity. Kpler said Iran began vetting ships and collecting money from those that pass. Ships must give cargo and crew details to the Islamic Revolutionary Guards Corps. Kpler said vessels must pay a USD 1 fee per barrel.

Kpler said US and Israeli vessels are barred, while some from Iran, India and China passed. It said India intervened diplomatically to get its vessels out. The White House demanded that Iran reopen the Strait. Central Command said the blockade is enforced impartially against vessels of all nations. It added warships warn of boarding and possible force.

US naval blockade against Iran: Economic pressure and Iran’s warning

The blockade could strain Iran’s economy, especially oil exports. Without exports, storage fills and wells may shut down, which can be hard to restart. Iran also imports petrol due to limited refinery capacity. Lloyd’s List Intelligence said the move created fresh uncertainty about what counts as neutral shipping. Neutral ships may pass, but may face inspections.

Iran’s joint military command issued a warning on Wednesday about wider disruption. "Iran would completely block exports and imports across the Persian Gulf region, the Sea of Oman and the Red Sea if the US does not lift its blockade on Iranian ports.\" Ali Abdollahi said, \"Iran will act with strength to defend its national sovereignty and its interests,\" and said the blockade risks the ceasefire.

With inputs from PTI