A U.S. Navy L3 Harris Arabian Fox MAST-13 drone boat and the U.S. Coast Guard cutters USCGC John Scheuerman and USCGC Charles Moulthrope transit the Strait of Hormuz on Wednesday, April 19, 2023. AP
The waters where the ship was seized, near the Strait of Hormuz, are a chokepoint for at least a third of the world's seaborne oil.
The "Marshall Islands-flagged oil tanker Advantage Sweet was seized by Iran's Islamic Revolutionary Guard Corps Navy while transiting international waters in the Gulf of Oman", the Bahrain-based US Fifth Fleet said in a statement.
"The Iranian government should immediately release the oil tanker," it added, slamming Tehran's "continued harassment of vessels and interference with navigational rights in regional waters".
The US Navy did not specify the owner of the vessel or its destination.
Iran and the United States have traded barbs in recent years over a spate of incidents in the sensitive waters of the Gulf.
The seizure on Thursday is just the latest incident in the Strait of Hormuz where ships have been mysteriously attacked, drones downed and oil tankers seized.
"In the past two years, Iran has unlawfully seized at least five commercial vessels sailing in the Middle East", the US Navy said.
In July 2019, the Revolutionary Guards seized the British-flagged oil tanker Stena Impero in the same waterway for allegedly ramming a fishing boat, and released it two months later.
Tensions have escalated since 2018 when then US president Donald Trump withdrew the United States from a multinational accord that froze Iran's nuclear programme, and reimposed crippling sanctions on its economy.