WASHINGTON - Russian military aircraft have conducted a series of “aggressive” overflights of a US destroyer in international waters in the Baltic Sea, a US defence official said Wednesday.

Speaking on condition of anonymity, the official described several incidents this week, including one on Tuesday in which a Russian Su-24 jet flew just 30 feet (nine meters) above the USS Donald Cook in a “simulated attack profile.”

“This is more aggressive than anything we’ve seen in some time,” the official said.

The manoeuvres began Monday while the destroyer was located about 70 nautical miles from Kaliningrad in International waters.

Two Russian Su-24s flew 20 times past the USS Cook at a distance of less than 1,000 yards (meters) and at an altitude of about 100 feet, the official said.

Then on Tuesday, a Russian Ka-27 Helix anti-submarine helicopter flew seven times around the destroyer, taking photographs as it passed. Shortly after, an Su-24 arrived and flew straight over the ship, “so low it created wake in the water,” the official said. The plane was “wings clean,” meaning it was not visibly armed.

US sailors tried multiple times to hail the Russian craft on international frequencies but got no response. “The commanding officer (of the Cook) - his assessment was that this was unsafe and unprofessional,” the official said of the overflights.

The incidents come at a time of heightened tension between Moscow and Washington over Russian involvement in conflicts in eastern Ukraine and in Syria.