Bulgaria launched naval manoeuvres in the Black Sea on Friday with six other NATO countries including the United States, in the latest demonstration of the alliance's resolve to support its eastern European members in light of the Ukraine crisis.
Bulgaria's defence ministry said the 10-day war games, dubbed BREEZE 2014, were designed to boost NATO solidarity and regional readiness, though it added they had been scheduled before Russia annexed Ukraine's Black Sea region of Crimea in March.
Vessels from Bulgaria and its Black Sea neighbours Romania and Turkey and also from Greece, Italy, Britain and the United States were due to take part in the exercises.
The drills will involve more than 1,000 Bulgarian marines, 15 ships and cutters, as well as two helicopters and two planes, the ministry said. A US guided missile cruiser and US aircraft are also involved in the exercises.
Russia's annexation of Crimea and its support for pro-Russian separatists in eastern Ukraine have triggered the worst crisis in relations between Moscow and the West since the collapse of the Soviet Union in 1991.
Bulgaria has traditionally had close ties with Moscow and was a loyal member of the Soviet-led Warsaw Pact alliance in communist times, but joined NATO in 2004 and the European Union in 2007 as part of a strategic reorientation towards the West.
The United States has stepped up military exercises with its eastern NATO allies in recent months in response to Russia's more assertive stance towards former Soviet republics.