Seven NATO members started a naval exercise in the Black Sea on March 10.
The naval rapid reaction force in the drills comprises a U.S. flagship, the guided-missile cruiser USS Vicksburg, and ships from the six other participating states -- Black Sea countries Turkey, Romania, and Bulgaria, plus Canada, Germany, and Italy.
NATO has held a series of exercises in eastern Europe, aimed in part to reassure members concerned about Russian intentions following Moscow's annexation of the Black Sea peninsula of Crimea in March 2014 and its moves in support of separatists fighting government forces in eastern Ukraine.
A Bulgarian navy spokesman said the training would include simulated antiair and antisubmarine warfare exercises, as well as simulated small boat attacks and basic ship handling maneuvers.
Last week, the defense ministry in Moscow said it had begun large-scale military exercises in southern Russia and in disputed territories including Crimea and Abkhazia, a breakaway, Moscow-backed region of Georgia on the Black Sea.