Iran's state news agency IRNA said on Saturday that its Revolutionary Guards had seized the MSC Aries vessel it said was "linked to Israel" and it was being transferred to Iran's territorial waters.
A Guards navy special forces helicopter boarded the Portuguese flagged vessel and seized it, IRNA added.
UK Maritime Trade Operations (UKMTO) said the vessel had been seized 50 nautical miles (92 km) northeast of the Fujairah, an area close to the Strait of Hormuz that forms the entrance to the Gulf.
A British maritime security company, Ambrey, reported a "boarding" incident at the same location but without giving further details.
Marine tracking sites said the vessel was the MSC Aries of Zodiac Maritime, an international shipping company partly owned by Israeli businessman Eyal Ofer.
Iran has threatened to retaliate for suspected Israeli airstrikes on its consulate in Syria's capital Damascus on April 1 that killed seven Revolutionary Guards officers including two senior commanders.
US President Joe Biden said on Friday he expected Iran to attack Israel "sooner, rather than later" and warned Tehran not to proceed.
