Pentagon officials say two Russian aircraft buzzed a U.S. Navy warship in the Arctic's Barents Sea last week, each coming within about 50 yards of the frigate.

Flybys of Navy ships in international waters are not unheard of. But the Cold War-style incident was unusual enough to raise eyebrows.

Pentagon spokesman Col. Dave Lapan said Navy personnel aboard the ship did not believe the actions were hostile. He told reporters on Friday that the U.S. was still trying to determine whether either side broke protocol.

Lapan said a Russian maritime patrol aircraft on Sept. 10 flew about 50 yards off the Navy frigate's side, as low as 100 feet. Lapan said a Russian helicopter did the same thing the next day.