Britain’s Royal Navy said on Thursday it had seized Iranian weapons, including anti-tank guided missiles, last month from a smugglers vessel in international waters in the Gulf of Oman. Britain said the vessel was detected travelling south from Iran at high speed during the hours of darkness by an unmanned U.S. intelligence surveillance and reconnaissance plane, and was also tracked by a British helicopter.

When hailed by the Royal Navy, the vessel initially attempted to navigate to Iranian territorial waters but was stopped by a team of Royal Marines, who then boarded the small boat and recovered the suspicious packages, Britain’s Ministry of Defence said.