A Russian fighter jet has made close-range passes for more than 90 minutes near a US warship in the Black Sea amid diplomatic tensions over Ukraine.
Pentagon said on Monday that the Russian Su-24 aircraft made 12 passes and flew within 900m of the destroyer USS Donald Cook on Saturday at about 150m above sea level.
"This provocative and unprofessional Russian action is inconsistent with international protocols and previous agreements on the professional interaction between out militaries," Army Colonel Steve Warren, a Pentagon spokesman, said.
The fighter appeared to be unarmed and never was in danger of coming in contact with the ship, said the officials, but it did not respond to radio queries and warnings used by the US warship.
Warren reported that a second Russian fighter jet was also involved, but it flew at a higher altitude and was not a concern.
A Russian navy frigate has also been shadowing the US warship, remaining within visual distance but not close enough to be unsafe, according to another anonymous US military official.
The USS Donald Cook was sent to the Black Sea on April 10 in the wake of the Russian military takeover of Crimea. A frigate from the US navy's sixth fleet is also heading to the Black Sea.
According to a US military official, the frigate is likely to replace the USS Donald Cook, which is expected to return to the Mediterranean Sea.