US Destroyer Donald Cook is to enter the Black Sea on April 10, Pentagon officials said.

The news came days after the White House announced its plans to extend the Black Sea mission of USS Truxtun, the first destroyer it sent there in March, and to deploy additional vessels.

Truxtun also took part in joint drills with Bulgarian and Romanian naval forces.

"We'll also send another ship to the Black Sea within a week," Derek Chollet, Assistant Secretary of Defense for International Security Affairs, was quoted as saying by the Department of Defense.

Spain-based USS Donald Cook set off for the Black Sea last week, in a move that the Pentagon said is to show US "support for Ukrainians" amid its standoff with Russia.

NATO member states declared last week plans to bolster security at the alliance's eastern borders, and to step up defense in Poland and the Baltic States.

Apart from Ukraine, three countries holding membership in the bloc - Bulgaria, Romania, and Turkey - also have a Black sea coastline.