Two commercial ships were hit by drones near Bulgaria's Black Sea coast early on October 13, with one sinking, leaving 11 crew members missing. Prime Minister Rumen Radev suggested Russia may be behind the attacks and summoned the Russian ambassador to Sofia.
It was the second time this month that commercial vessels have been struck in Bulgaria's Black Sea exclusive economic zone (EEZ). Earlier, on October 6, the cargo ship Alfa Watan sank following a drone attack, with all 10 crew members logged as missing, while the vessel Able was damaged and its crew rescued.
The latest incidents have heightened concerns over the spread of the war between Russia and Ukraine towards Bulgaria's coast and vital Black Sea shipping routes.
The Maltese-flagged Chelsea 3, a Ukrainian-owned cargo ship, was struck by three aerial drones about 18 nautical miles (33 km) east of the coastal town of Byala early on October 13, Radev announced in a televised address. All 15 crew members, seven Ukrainians and eight Azerbaijanis, were evacuated to the Bulgarian port of Varna. Five received medical treatment.
The second vessel, identified by Bulgarian President Iliana Iotova as the Guinea-Bissau-flagged cargo ship HS Dignity, sank about 17 nautical miles east of Krapets, near the Romanian border. Eleven crew members remained missing, while a search and rescue operation continued.
"Another attack on commercial vessels in the immediate vicinity of Bulgarian territorial waters is absolutely unacceptable," Radev said after convening an emergency meeting of the government's Security Council, Bulgarian National Radio (BNR) reported.
Radev said there was no conclusive evidence identifying those responsible, but the outcome of the attacks appeared to benefit Russia. He summoned Russian Ambassador Eleonora Mitrofanova to discuss the incidents.
Mitrofanova said she had no information from Russia's defence ministry about the attacks and suggested they could have been a provocation by a third party, Bulgarian media reported.
Bulgaria has sought assistance from its allies to investigate the attacks. Radev said he had spoken to European Commission President Ursula von der Leyen and Nato Secretary-General Mark Rutte, calling for coordinated efforts to stop attacks on commercial shipping.
Rutte said Nato would continue working with its Black Sea allies and adjust its deterrence and defence posture as needed.
"The Black Sea has become another front of escalation of the Russian war in Ukraine," von der Leyen said on social media, condemning the attacks and calling for those responsible to be held accountable.
Iotova said the escalation was turning the Black Sea into a military zone, threatening freedom of navigation and supply-chain security. She called for a swift investigation and diplomatic efforts to de-escalate the conflict.
Bulgaria's opposition parties called for a stronger response, with some demanding an emergency parliamentary sitting and others urging closer coordination with Nato.
Defence Minister Dimitar Stoyanov said the conflict was drawing closer to Bulgaria's territorial waters and that Russia was the likely source of the drones, arguing that Ukraine would have little reason to target its own ships.
Ukraine has also blamed Russia for the latest attacks. Moscow has not publicly commented on the incidents.
Russia and Ukraine are major grain exporters, making the Black Sea a crucial route for agricultural shipments and other commercial trade.