Russian warplanes have made several "aggressive" passes near a US guided missile destroyer, according to US military sources. The jets carried no visible weapons but failed to respond when hailed, officials say.
The pilots flew "dangerously close" to the US destroyer Donald Cook in Baltic Sea, White House spokesman Josh Earnest said on Wednesday.
According to US military officials, two Russian Su-24 jets began maneuvering near the ship on Monday, flying at an altitude of some 100 feet (30 meters). The ship allegedly had a Polish helicopter on board, and was located in international waters, some 70 nautical miles (130 kilometers) from the Russian exclave Kaliningrad.
On Tuesday, a Russian anti-submarine helicopter circled and photographed the vessel, followed by a jet flying straight above the ship. The apparently unarmed Su-24 passed just 30 feet (nine meters) above the destroyer, according to a senior US official.
"This is more aggressive than anything we've seen in some time," he said.
US military's Europe Command (EUCOM) published several videos allegedly showing the "unsafe and unprofessional" maneuvers.
"The Russian aircraft flew in a simulated attack profile and failed to respond to repeated safety advisories in both English and Russian," EUCOM said.
"These actions have the potential to unnecessarily escalate tensions between countries, and could result in a miscalculation or accident that could cause serious injury or death," they added.
USS Donald Cook was not engaged in formal military exercises at the time.
The incident comes amid military tensions between NATO and Moscow, prompted by the outbreak of the Ukraine conflict in 2014. NATO is currently planning its largest military build-up in the Baltic and Poland since the Cold War.