A Liberia-flagged container ship was struck by drones in the Black Sea off Bulgaria's northern coast on October 28, the defence minister said, the latest in a series of attacks on merchant vessels in the region.

The incident is the latest in a series of drone attacks on commercial vessels in the Black Sea, with at least six merchant ships attacked in recent weeks. The attacks have raised concerns about the widening impact of Russia's war in Ukraine on maritime security.

The Greek-owned Contships Jet, sailing under the Liberian flag from Haifa, Israel, to the Romanian port of Constanța, was hit by three drones in Bulgaria's exclusive economic zone, about 21 nautical miles southeast of Shabla, Defence Minister Dimitar Stoyanov said, Bulgarian media reported. The crew was reportedly evacuated, according to Reuters.

Ukraine has blamed Russia for the recent series of attacks, while Bulgarian Prime Minister Rumen Radev has said they appear to benefit Moscow. Russia has denied involvement.

Bulgaria, Romania and Turkey condemned the attacks in a joint statement, calling for an immediate halt to actions threatening commercial shipping and maritime activities.

"These tragic incidents represent a dangerous escalation of tensions and pose serious risks to maritime security," Stoyanov said, BGNES reported.

The three Nato members agreed to establish a trilateral coordination mechanism to improve information-sharing, early warning and their response to security threats in the Black Sea, Stoyanov said.

Stoyanov also said the cargo ship Khoryv, which capsized following a military attack, was drifting towards and entering Bulgarian territorial waters. The Bulgarian navy and transport ministry were monitoring the situation, and a navigational warning had been issued to vessels in the area.