A oil tanker owned by the United Kingdom was seized on Friday by Iran’s Islamic Revolutionary Gard Corps in the Strait of Hormuz amid increasing tensions in the region.

The British vessel Stena Impero, which had 23 crew members onboard, “was approached by unidentified small crafts and a helicopter during transit of the Strait of Hormuz while the vessel was in international waters. We are presently unable to contact the vessel which is now heading north towards Iran,” according to Stena Bulk and Northern Marine Management.

U.K. Defense Secretary Penny Mordaunt has been briefed on the incident, reported Sky News.