Two Russian warplanes flew simulated attack passes near a US guided missile destroyer in international waters in the Baltic Sea on Tuesday, US military said.
During series of aggressive flights by the Sukhoi SU-24, the warplanes created wake in the water, with 11 passes, the official said. They also flew near the ship a day earlier.
A Russian KA-27 Helix helicopter also made seven passes around the USS Donald Cook, taking pictures. The nearest Russian territory was more than 100 nautical kilometres away in its enclave of Kaliningrad, which sits between Lithuania and Poland.
The planes carried no visible weaponry, while a senior US defence official described the interaction as the most aggressive in recent memory.
"They tried to raise them (the Russian aircraft) on the radio but they did not answer," the official said, speaking on condition of anonymity, adding the US ship was in international waters.
US military's European Command (EUCOM) released a video showing warplanes zooming so close past the Cook that one sailor can be heard saying: "He is below the bridge wing," meaning the plane was flying lower than the highest point of the ship.
"We have deep concerns about the unsafe and unprofessional Russian flight manoeuvres," EUCOM said in a statement.
"These actions have the potential to unnecessarily escalate tensions between countries and could result in a miscalculation."
US-Russia relations are in the grip of political conflict over Moscow's involvement in eastern Ukraine and in Syria in opposite direction of its Cold War foe.
The incident also came as NATO plans its biggest build-up in eastern Europe since the Cold War to counter what the alliance, and in particular the three Baltic states and Poland, consider to be a more aggressive Russia.
The Baltic states, Estonia, Latvia and Lithuania, which joined both NATO and the European Union in 2004, have asked NATO for a permanent presence of battalion-sized deployments of allied troops in each of their territories. A NATO battalion typically consists of 300 to 800 troops.
Moscow denies any intention to attack the Baltic states.
The Pentagon periodically decries the risky tactics displayed by Russian pilots.
"There have been repeated incidents over the last year where the Russian military, including Russian military aircraft, have come close enough to each other or have come close enough to other air and sea traffic to raise serious safety concerns," White House Press Secretary Josh Earnest said.
Exactly two years ago -- on April 12, 2014 -- a Russian Su-24 made numerous close-range, low-altitude passes near the USS Donald Cook while it was in the Black Sea, in an incident the Pentagon at the time called a "provocative act."