A drone attack sank a ship off Bulgaria’s Black Sea coast on Tuesday, while another vessel was also hit, Bulgarian Prime Minister Rumen Radev said.According to Reuters, the Maltese-flagged vessel Chelsea 3, which is owned by a Ukrainian company, was struck by three drones about 18 nautical miles off Bulgaria’s coast. All 15 crew members aboard the ship were rescued, while the second vessel sank in the attack.Bulgarian Prime Minister Rumen Radev said there was no clear evidence identifying those responsible for the attacks, describing the incident as the second of its kind in a week.“This is absolutely unacceptable — another attack in the immediate vicinity of Bulgarian territorial waters,” Radev said, adding that he would speak with Nato secretary-general Mark Rutte.In an earlier incident on October 6, drones struck two merchant ships in Bulgaria’s exclusive economic zone in the Black Sea.The Togo-flagged cargo ship Alfa Watan sank, while the vessel Able, which was carrying grain, was damaged. Ukrainian President Volodymyr Zelenskyy blamed Russia for that attack.Russia denied involvement in the attack, with its embassy in Sofia saying the merchant vessel Alfa Watan was not among the targets hit by Russian drones. The Russian defence ministry said the origin of the drones would need to be established through an investigation.The attacks have raised concerns over the security of commercial vessels operating near Bulgaria, a member of the North Atlantic Treaty Organisation (Nato).The Black Sea remains a crucial route for grain and other commodities, particularly for Ukraine, and repeated strikes on merchant ships could disrupt maritime trade and increase risks for shipping operators.