The confrontation escalates an already volatile situation around one of the world’s most critical waterways. Iran has effectively closed the Strait of Hormuz to normal shipping since the onset of the U.S.-Israel conflict, cutting off roughly 20% of the world’s typical daily oil consumption and pushing energy prices higher. The U.S. counter-blockade, which began Monday, now threatens to choke Iran’s economy from the other direction — but risks widening a conflict that has already killed civilian mariners.
FRANKFURT — The U.S. Navy’s sea blockade against Iran showed early signs of effectiveness Wednesday, with U.S. Central Command reporting that no vessel broke through during the first 48 hours of the operation and that 10 ships had turned around and returned toward Iranian waters.
“The blockade has been fully implemented,” said Adm. Brad Cooper, head of U.S. Central Command. “U.S. forces have completely halted economic trade going in and out of Iran by sea.”
The blockade, which began Monday, is being enforced in the Gulf of Oman beyond the Strait of Hormuz. It applies to vessels leaving Iranian ports and coastal areas. U.S. Navy warships have told merchant ships they are prepared to board them and use force to compel compliance, according to the Associated Press.
Ships turning around, responses uneven
Shipping data firms confirmed that Iran-linked or sanctioned vessels that transited the Strait of Hormuz have largely halted or reversed course. On the first full day of the blockade Tuesday, only eight vessels — most of them linked to Iran or carrying sanctioned cargo — transited the strait, said Ana Subasic, trade risk analyst at data firm Kpler.
“Most of the vessels have appeared to halt or have reduced movement after clearing the strait,” Subasic said, “which tells us that the effect of the blockade is starting to show up because most of these vessels that have crossed have some kind of history with carrying Iranian-origin sanctioned cargo.”
The environment remains “extremely high risk” despite a ceasefire, she said.
One tracked vessel illustrated both the blockade’s reach and its complications. The Rich Starry — a Chinese-owned tanker sailing under the flag of Malawi and previously sanctioned by the U.S. for smuggling Iranian petroleum products — had turned off its radio transponder for more than a week before reappearing off the United Arab Emirates loaded with oil. The ship transited the strait Monday night, then abruptly reversed course in the Gulf of Oman on Tuesday and headed back toward Iran’s coast, according to publicly available ship tracking data.
Maritime intelligence firm Windward described the overall pattern as “indicating a fragmented and uneven response to the blockade,” with sanctioned and false-flagged vessels continuing to be active, some reversing course and others delaying or transiting before halting.
Enforcement rules and industry uncertainty
The blockade applies to vessels departing from Iranian ports and coastal areas, not to all ships passing through the strait itself. A notice to mariners specifies that the blockade is enforced in the Gulf of Oman and the Arabian Sea, meaning a vessel can clear the strait and still face interception farther out.
Humanitarian shipments — including food and medical supplies essential for civilian survival — may pass with inspections, per the blockade’s terms. Maritime historian Sal Mercogliano noted that provision aligns with international law on naval warfare, which bars blockades solely intended to starve civilians.
The scope of the exemptions has added to industry confusion. Lloyd’s List Intelligence maritime data firm said the U.S. action “has plunged shipowners into fresh uncertainty around enforcement.”
A U.S. official, speaking on condition of anonymity to discuss sensitive military operations, said the Navy relies on more than the automated tracking beacons — known as AIS — that all merchant ships are required to carry, without specifying additional methods. Some vessels appeared to have transmitted false location coordinates, a tactic known as spoofing, the AP reported.
Iran’s strait closure and counter-blockade threat
The U.S. blockade is a response to Iran’s effective closure of the Strait of Hormuz. Iran has blocked the strait by threatening to attack shipping, cutting off roughly 20% of the world’s typical daily oil consumption. Aerial and undersea drone strikes and other projectiles have killed 11 crew members aboard vessels in the area, and ship traffic through the strait has dropped by more than 90%.
Iran has also begun extracting economic benefit from the handful of vessels willing to navigate the chokepoint, vetting ships and collecting a fee of $1 per barrel of oil or fuel products through its paramilitary Revolutionary Guard before granting passage, according to Kpler.
The U.S. blockade threatens to inflict serious damage on Iran’s economy in return. Without oil exports, Iran’s available storage would fill up, forcing the country to shut down wells that are difficult to restart. Iran also imports gasoline because it lacks the domestic refinery capacity to process its own crude into fuel.
Ali Abdollahi, commander of Iran’s joint military command, warned Wednesday that Tehran would act if Washington does not lift the blockade. “Iran will act with strength to defend its national sovereignty and its interests,” Abdollahi said, warning that Iran would “completely block exports and imports across the Persian Gulf region, the Sea of Oman and the Red Sea.” He called the U.S. blockade “a prelude to violating the ceasefire.”
Some oil from Gulf producing nations is moving through pipelines to the Red Sea and the Gulf of Oman, partially bypassing the closed strait. Those pipelines cannot compensate for the volume ordinarily flowing through the Strait of Hormuz, according to the AP.