An official from the European Union’s naval mission Aspides said on Saturday that commercial vessels have received radio warnings stating that no ship is allowed to pass through the Strait of Hormuz.

The warnings were transmitted over VHF radio and attributed to the Islamic Revolutionary Guard Corps, the official said, speaking on condition of anonymity.

However, the official stressed that Iran has not formally confirmed any decision to restrict or block shipping in the narrow waterway.

The Strait of Hormuz is the world’s most critical oil transit chokepoint, linking major Gulf oil producers — including Saudi Arabia, Iran, Iraq and the United Arab Emirates — with the Gulf of Oman and the Arabian Sea.

Tehran has repeatedly threatened over the years to close the Strait in response to military action against the Islamic Republic, though it has never followed through on the threat.