Fears are growing over the fate of Syrian and Egyptian sailors aboard the HS Dignity, a Guinea-Bissau-flagged cargo vessel that sank following a suspected Russian attack off the coast of Bulgaria on Tuesday.
The Syrian Sailors' Union announced that the vessel, which had 16 crew members on board, 14 Syrians and two Egyptians, sank following an attack involving an aerial drone and two unmanned boats.
The ship was travelling between Algeria and the Romanian port of Braila with a crew of Syrian and Egyptian nationals, according to the Bulgarian interior ministry.
The incident comes less than a week after another ship carrying Syrian sailors sank in the same area of the Black Sea.
The Syrian Sailors' Union said search and rescue teams had managed to save five crew members, while the search continued for the remaining 11. Six boats and two helicopters were taking part in the operation.
The union added that it was monitoring developments in coordination with search and rescue authorities and the ship's owner to obtain accurate information about the fate of the missing sailors.
On Tuesday, Bulgarian authorities also reported that a third vessel, the Ukrainian-owned Chelsea 3, had been attacked by drones. Its entire crew of 15 sailors, including seven Ukrainians, was evacuated.
Bulgarian Prime Minister Rumen Radev summoned the Russian ambassador following the drone attacks.
Radev said the Chelsea 3 was "hit by three aerial drones", and that shortly afterwards, the HS Dignity was "struck" and sank.
"We lack solid, clear evidence to level accusations against any specific party; however ... logic suggests the outcome works to the advantage of the Russian Federation," he wrote, calling the attack "unacceptable".
Fears grow for Syrian shipping workers
The sinking of the HS Dignity has heightened fears among families of Syrian sailors working aboard commercial vessels, particularly amid repeated attacks on ships in the Black Sea.
Shipping routes near conflict zones have become increasingly dangerous for civilian crews who are not involved in military operations.
About a week earlier, on 6 October, the Alpha Vatan, a Togolese-flagged vessel, was attacked by suspected Russian aerial and naval drones in Bulgaria's exclusive economic zone in the Black Sea.
The attack caused the ship to sink, leaving its crew missing. According to Syrian authorities, ten sailors were aboard the vessel, nine Syrians and one Egyptian.
Moscow denied responsibility for the attack.
On 7 October, Bulgarian authorities announced that they were suspending the search for the Alpha Vatan's crew after rescue teams failed to find any survivors.
The following day, Mazen Alloush, Director of International Relations and Cooperation at Syria's General Authority for Border Crossings, announced that Syrian authorities had sent official memoranda to Bulgaria and the International Maritime Organisation, calling for an investigation into the incident and clarification of the sailors' fate.
Alloush stressed the need for an independent and transparent investigation, expressing Damascus's concern over the suspension of search and rescue operations before conclusive information about the crew's fate had been obtained.
The families of the missing sailors continue to await definitive information about their loved ones, while the sinking of another ship carrying Syrian crew members has raised further concerns over the safety of maritime workers in the Black Sea.
Amid the Russia-Ukraine war, both sides have used aerial and maritime drones to target military and economic assets. The growing threat to commercial shipping has increased the risks faced by civilian crews uninvolved in the conflict.
Agencies contributed to this report.