Iran warned the U.S. against targeting a supertanker carrying the Middle East country's oil as the vessel departed Gibraltar after being seized last month by U.K. forces and held in the British territory.

The tanker, detained by the British on suspicion of hauling oil to Syria in violation of European sanctions, set sail from Gibraltar after being released late last week and is signaling Greece as its next destination.

"The U.S. surely can't seize the Iranian tanker and, if it does, it would pose a threat to international maritime security," Iranian Foreign Ministry spokesman Abbas Mousavi said. Iran warned the U.S. via "diplomatic channels," including Switzerland, against interfering with the tanker, formerly known as Grace 1, in international waters, Mousavi said at a news conference in Tehran. Swiss diplomats serve as interlocutors between the U.S. and Iran.