WASHINGTON -- The Pentagon said a Russian aircraft made about a dozen low level flights near a U.S. Navy warship in the Black Sea, calling the actions "provocative."

The USS Donald Cook, a guided missile destroyer, was conducting routine operations in the western Black Sea on Saturday when the Russian attack aircraft flew near the ship and did not respond to multiple warnings from the American warship.

The incident comes amid heightened tensions between the United States and Russia over Russia's actions in Ukraine.

The Russian Su-24 flew close by but not directly over the American ship, the Pentagon said.

The incident took 90 minutes during which the Americans repeatedly queried the Russians but received no response.

The Pentagon said in a statement Monday that the Russian aircraft was unarmed and never posed a threat to the American warship, but the actions were "unprofessional" and "provocative."

White House spokesman Jay Carney said Monday that President Obama expects to speak "soon" with Russian counterpart Vladimir Putin by phone, "perhaps today."

Contributing: David Jackson