A commercial vessel was struck by drones near Bulgaria's Black Sea coast overnight on Oct. 13, Bulgarian Prime Minister Rumen Radev said.
According to Radev, the Maltese-flagged Chelsea 3, registered in Odesa and owned by a Ukrainian company, was hit by three aerial drones about 18 nautical miles east of the coastal town of Byala in Bulgaria.
All 15 crew members, seven Ukrainians and eight Azerbaijani nationals, were evacuated to the port of Varna, and five received medical assistance, Radev said.
He added that another vessel was struck 17 nautical miles east of Krapets, a Bulgarian village, as he was told at an extraordinary meeting of the Security Council under the Council of Ministers. The vessel sank, and one crew member was rescued.
Radev called the attacks "absolutely unacceptable" and said Bulgaria had informed its permanent representatives to NATO and the European Union. Sofia is seeking assistance to strengthen surveillance of the air and maritime domains and improve its response capabilities.
Bulgarian authorities have not established who was responsible for the attacks. Radev said there was no clear and conclusive evidence to attribute responsibility to either the Ukrainian or Russian side, but argued that "the logic suggests that the outcome benefits the Russian Federation." Radev said he would summon Russia's ambassador for a meeting on Oct. 13.
European Commission President Ursula von der Leyen condemned the attacks, saying the Black Sea had become "another front of escalation of the Russian war in Ukraine."
"Putting the lives of the crew in grave danger and threatening security in the Black Sea. We stand with Bulgaria and thank its rescuers for their swift response."
Ukraine's Infrastructure Ministry said Russia has repeatedly targeted Ukrainian ports, port infrastructure, and civilian commercial vessels in the Black Sea, posing a threat to international shipping and logistics routes.
Attacks by Ukraine and Russia in the Black Sea intensified over the summer.
In July, Ukraine launched Operation Molochka, a campaign targeting Russia's shadow fleet in the Black Sea and the Sea of Azov in an effort to tighten the noose around Russian-occupied Crimea.
Turkey called on Moscow and Kyiv in August to impose a moratorium on attacks against vessels, following a series of strikes in the region that involved Turkish-flagged ships.
While Kyiv has said it is ready to accept a moratorium on attacks in the Black Sea, Moscow has shown no interest in de-escalating the situation.
On Aug. 6, drones reportedly struck several merchant vessels in the Black Sea, including two ships in Bulgaria's exclusive economic zone. A Russian strike on a separate civilian vessel that day killed at least one crew member and injured several others.
Ukraine established its own Black Sea maritime corridor in August 2023, after Russia withdrew from a U.N.- and Turkey-brokered grain deal. Since then, Russia has regularly targeted ports and civilian shipping.