Sea and aerial drones struck two commercial vessels about 80 miles off Bulgaria’s Black Sea coast on Tuesday, sinking one of them, in the first such attack on shipping in a NATO member’s exclusive economic zone. Prime Minister Rumen Radev called it a blatant violation of international law.

The Togo-flagged Alfa Watan suffered critical structural damage and sank, and its crew remained missing on Tuesday morning. The Palau-flagged Able, carrying wheat, caught fire after the attack. A Bulgarian ferry evacuated all 18 crew members, including 11 Turks and seven Indians. Two sailors were flown to a hospital in the port city of Varna with severe injuries.

The origin of the drones has not been established, and Russia did not immediately comment. Radev said the war was expanding geographically and increasing the risk of global conflict. The attack came a day after a cargo ship carrying Ukrainian corn sank off Romania. Authorities were monitoring for possible oil spills and other environmental pollution.