A U.S. guided-missile destroyer is en route to the Black Sea but naval officials said Thursday it was a "routine" deployment that was planned before the crisis unfolded in Ukraine.

The USS Truxtun departed the Greek port of Souda Bay Thursday to carry out joint training with Romanian and Bulgarian forces, the U.S. Navy said in a statement.

"While in the Black Sea, the ship will conduct a port visit and routine, previously planned exercises with allies and partners in the region," it said.

The mission was "scheduled well in advance of her departure from the United States," it said.

Although portrayed as unrelated to tensions in Ukraine, where pro-Russian forces have taken de facto control over the Crimean peninsula, the presence of a US naval destroyer in the Black Sea sends a symbolic message to Moscow.

The move comes a day after the Pentagon sought to reassure anxious allies in Central and Eastern Europe over Russia's actions in Ukraine, announcing plans to send more F-15 fighter jets to patrol the skies over Baltic states and stepping up aviation training in Poland.

At the moment, the only US naval ship deployed in the Black Sea is the USS Taylor, a frigate undergoing repairs at the Turkish port of Samsun after having run aground last month.

The Truxtun is part of the George HW Bush aircraft carrier strike group currently assigned to the U.S. Navy's 6th fleet, which oversees operations in the Mediterranean.