Iran's naval commandos seized a Barbados-flagged tanker Ocean Koi in the Sea of Oman in a special operation, Iranian state media reported on Friday.
Tehran accused the vessel of attempting to disrupt Iranian oil exports.
Maritime intelligence firm TankerTrackers separately reported that three empty National Iranian Tanker Company vessels had crossed the U.S. Navy blockade line over the past two days through Pakistan's Exclusive Economic Zone (EEZ).
The Iranian Army's public relations confirmed the operation across state media outlets, including Tasnim, Fars and IRNA, saying: "In a special operation, the naval commandos of the Islamic Republic of Iran's Army seized the violating tanker Ocean Koi, which was seeking to cause disruption to Iran's oil exports and the interests of the Iranian nation."
According to IRNA and the Army's official statement, the ship was carrying Iranian oil cargo and was exploiting regional conditions to harm Iran's oil exports.
The IRGC naval commandos and marines guided the vessel to Iran's southern coast and handed it over to judicial authorities.
"The operation was carried out under a decision of the Supreme National Security Council and a judicial order," the statement said.
Open-source monitoring indicated the Iranian Navy used domestic speedboats in the boarding operation, with personnel appearing to be armed with AK-103/KL-103 assault rifles.
The Iranian Navy said it "will resolutely defend the interests and assets of the Iranian nation in the country's regional waters and will not tolerate any violator or aggressor."
Separately, TankerTrackers said on Friday that three empty crude tankers belonging to the National Iranian Tanker Company had crossed through the U.S. Navy blockade line over the past two days, using Pakistan's EEZ as a transit corridor to return to Iran.
The three vessels have a combined crude-carrying capacity of 5 million barrels.
Two tankers were confirmed on satellite imagery, with their identities shared with TankerTrackers clients. A third vessel, the Hasna, appeared on the Automatic Identification System (AIS) data late Thursday off the coast of Shinas, Oman, approximately 254 nautical miles (470 kilometers) west of the blockade line, though visual confirmation remained pending.
Hasna's appearance was notable given that U.S. Central Command (CENTCOM) announced that U.S. forces had disabled the rudder of the Iranian-flagged M/T Hasna in the Gulf of Oman after its crew allegedly failed to comply with repeated warnings during an interception.
CENTCOM said the vessel was unladen and transiting toward an Iranian port. "Hasna is no longer transiting to Iran," CENTCOM said at the time. Ship-tracking databases list the Hasna as a 333-meter Iranian-flagged crude tanker built in 2003 and subject to U.S. sanctions.