WASHINGTON — A Russian fighter aircraft made repeated low-altitude, close-range passes near a U.S. ship in the Black Sea over the weekend, the Pentagon said on Monday, condemning the action at a time of heightened U.S.-Russian tensions over Ukraine.

"This provocative and unprofessional Russian action is inconsistent with their national protocols and previous agreements on the professional interaction between our militaries," said Colonel Steve Warren, a Pentagon spokesman.

Warren said a Russian Su-24 aircraft, or Fencer, made 12 passes at low altitude near the USS Donald Cook, a destroyer that has been in the Black Sea since April 10. It appeared to be unarmed, he said.

At the time the passes took place, Warren said, the U.S. ship was conducting a patrol in international waters in the western Black Sea. It is now in a Romanian port.