NATO troops make a massive amphibious landing off the coast of Ustka, northern Poland, during NATO military sea exercises BALTOPS (Baltic Operations) 2015 in the Baltic Sea. (AFP PHOTO)

MOSCOW, Apr. 18 (Xinhua) -- Russia's Baltic Fleet forces are monitoring movements of ships of the North Atlantic Treaty Organization (NATO), which have entered the sea area, the Russian Defense Ministry said Thursday.

It said in a statement that earlier in the day, a NATO naval group consisting of U.S. destroyer Gravely, frigates General Kazimierz Pulaski of Poland, Gokova of Turkey and Almirante Juan de Bourbon of Spain entered the Baltic Sea.

The Russian Baltic Fleet has put on the alert duty ship strike groups, coastal Bastion and Bal and naval aircraft in order to promptly respond to possible emergency situations, the statement said.