SOFIA, Bulgaria: Eleven sailors were missing on October 13 after a cargo ship sank in a drone attack off Bulgaria's Black Sea coast, raising fears of another deadly incident involving commercial vessels in the area within a week.

Bulgarian officials said drones hit two cargo ships overnight, sinking one. The government did not directly accuse Russia of carrying out the attacks, but Prime Minister Rumen Radev said the outcome benefited Moscow.

"This is absolutely unacceptable — another attack in the immediate vicinity of Bulgarian territorial waters," Radev said in a televised address.

Bulgaria summoned Russia's ambassador, Eleonora Mitrofanova, following the incidents. Moscow had not issued an immediate official response.

Ukraine and the European Union also condemned the strikes. European Commission President Ursula von der Leyen said the Black Sea had become another area of escalation in Russia's war against Ukraine and called for those responsible to be held accountable.

Ukraine's Foreign Minister Andrii Sybiha accused Moscow of showing disregard for civilian lives. He also warned that attacks on Black Sea shipping threatened global food security, as both Russia and Ukraine are major grain exporters.

Bulgarian authorities said five crew members had been rescued from the ship that sank near the coastal village of Krapets, while 11 remained missing.

President Iliana Iotova identified the vessel as the HS Dignity, a cargo ship sailing under the Guinea-Bissau flag. Search and rescue operations were continuing.

Bulgarian officials said a second vessel, the Chelsea 3, which sails under the Maltese flag, was also struck by three drones overnight.

Rescuers saved all 15 crew members on that ship. They included seven Ukrainians and eight Azerbaijanis, and none suffered serious injuries.

The latest attacks came about a week after another cargo ship sank in Bulgaria's Black Sea exclusive economic zone following a drone strike. Nine Syrian sailors and one Egyptian crew member were lost at sea in that incident. A second ship was also hit that night, but rescuers saved its crew.

The repeated attacks have raised concerns about the safety of commercial shipping near Bulgaria and other Black Sea-bordering countries.

Bulgaria Seeks NATO Support

Following the latest incidents, Radev spoke by telephone with von der Leyen and NATO Secretary General Mark Rutte. He asked for their support in strengthening Bulgaria's monitoring of its maritime territory and airspace, according to a statement from the Bulgarian government.

Rutte said NATO would continue to adjust its military presence along its eastern flank as needed.

After meeting Radev in Sofia, Russian Ambassador Mitrofanova said she had received no information from Russia's Defense Ministry about attacks on commercial vessels in the Black Sea. She also suggested that a third party could have been responsible for the incidents, according to the Bulgarian government's account.

The Russian government had not provided further details or publicly accepted responsibility for the attacks.

The latest incidents highlight the growing risks to commercial shipping more than four and a half years after Russia launched its full-scale invasion of Ukraine in 2022.

The Black Sea is a vital route for transporting grain and other goods. Russia and Ukraine are among the world's largest grain exporters, so the security of shipping routes matters for international food supplies.