Two commercial vessels were struck by drones on Tuesday, October 6, in Bulgaria’s exclusive economic zone in the Black Sea — the first attack on shipping in the exclusive economic zone of a North Atlantic Treaty Organization (NATO) member, according to CBC News.

The Togo-flagged Alfa Watan suffered critical structural damage and sank, and the crew’s fate remains unknown. The second ship, registered in Palau, caught fire and its Turkish and Indian crew members were rescued, according to RFI. Bulgaria’s prime minister said, according to CBC News, that the situation is seriously disrupting shipping in the Black Sea, driving up insurance costs even further and making shipping extremely difficult.