A US military aircraft has patrolled over the Black Sea because of the tense security situation, the defence ministry told the Bulgarian news agency BTA in reply to a query.

The patrol is part of stepped-up vigilance in the Black Sea region, the ministry said.

Bulgaria has asked its NATO allies for patrol aircraft, missile systems and anti-drone systems, defence minister Dimitar Stoyanov said last week. He sent the request in letters to NATO secretary general Mark Rutte and to NATO's Supreme Allied Commander Europe, Alexus Grynkewich.

The aim is to boost capabilities, at least to show strength on Bulgarian territory and in Bulgaria's territorial waters, Stoyanov said. Bulgaria has asked for the full range of options and is waiting for a decision.

Drones are now also watching the Black Sea coast, the defence ministry said yesterday. It said this is part of precautionary steps to improve security and to get timely information on the situation in the area.

In the past month, four ships have been attacked in Bulgaria's exclusive economic zone in the Black Sea. Two of them sank.

Follow-up: Poseidon plane in Varna is for surveillance and will not strike targets