The tanker, Niovi, was sailing from Dubai towards Fujairah, another port in the United Arab Emirates, when it was stopped by Iran's Islamic Revolutionary Guard Corps Navy.

"A dozen IRGCN fast-attack craft swarmed the vessel in the middle of the strait," said a statement from the Bahrain-based US Fifth Fleet, referring to the Revolutionary Guard's naval force.

Six days ago, Iran's navy seized a Marshall Islands-flagged oil tanker in the Gulf of Oman, a nearby waterway also bordering the Arabian Peninsula and Iran.

The troubled but commercially vital Gulf waters, which carry at least a third of the world's seaborne oil, have witnessed a spate of incidents since 2018, when then US president Donald Trump pulled out of a nuclear agreement and reimposed crippling sanctions on Iran.

Iran has harassed or attacked 15 internationally flagged merchant vessels in the past two years, the US Navy said, calling its actions "contrary to international law and disruptive to regional security and stability".

"Iran's continued harassment of vessels and interference with navigational rights in regional waters are unwarranted, irresponsible and a present threat to maritime security and the global economy," it added.