The Iranian Revolutionary Guard claimed to have seized a British oil tanker in the Strait of Hormuz on Friday, The Guardian reports. The tanker, the Stena Impero, reportedly went off course “suddenly” and headed to Iranian waters. Stena Impero’s owners said the ship was “approached by unidentified small crafts and a helicopter during transit of the Strait of Hormuz while the vessel was in international waters,” and they have been “unable to contact the vessel,” which was originally en route to Saudi Arabia. In a statement, the Revolutionary Guard said it was seized for “non-compliance with international maritime laws and regulations.”

A spokesman for the U.K.’s Ministry of Defense told The Telegraph it was “urgently seeking further information and assessing the situation following reports of an incident in the Gulf.” A British official told The Daily Beast the issue was being discussed in the highest levels of the British government. U.S. National Security Council spokesman Garrett Marquis said they were “aware” of reports regarding the seizure. “The U.S. will continue to work with our allies and partners to defend our security and interests against Iran’s malign behavior,” he said. This comes after Iran denied that the U.S. shot down one of its drones in the Strait of Hormuz. President Trump said the Iranian drone was “destroyed” in a defensive move on Thursday.