An oil tanker was boarded by armed individuals near the Gulf of Oman on Thursday and appeared to change course toward Iranian waters, according to the U.K. Marine Trade Operations.

The UKMTO reported on social media that an unnamed ship was boarded by four or five unauthorized people early Thursday at 50 nautical miles east of Sohar, Oman.

“Unauthorised boarders are reported to be wearing military style black uniforms with black masks,” the UKMTO said, adding that the vessel “has altered course towards Iranian territorial waters and communications with the vessel have been lost.”