Two Russian warplanes flew close to a US guided missile destroyer almost a dozen times, the BBC has reported, citing American officials.
The Sukhoi SU-24 warplanes, in international waters in the Baltic Sea, had no visible weaponry and the ship took no action, the report said.
American officials are said to have called the events on Monday and Tuesday "one of the most aggressive acts in recent memory".
The commander of the missile destroyer, the USS Donald Cook, reportedly described the flights as a "simulated attack".
American officials described the Russian passes as "unsafe, potentially provocative" and "could have caused an accident".
Aside the Russian warplanes, a Russian helicopter taking pictures also passed by the ship seven times, the report said.
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