Multiple Russian aircraft buzzed a U.S. destroyer patrolling in the Black Sea last week, in an incident the captain of the American ship called “unsafe,” the Pentagon said Tuesday.

The three flybys occurred on Feb. 10 and were first reported by the Washington Free Beacon.

Lt. Col. David Faggard, a U.S. European Command spokesman, said the USS Porter, an Arleigh Burke-class guided missile destroyer, was returning from an exercise off the coast of Romania when an Il-38 sub-hunting twin-engine aircraft approached at a high speed and low altitude. The Il-38 was followed by two Su-24 fighter-bomber jets and then a single Su-24.

Faggard said the aircraft did not respond to radio calls and that they did not have their identification transponders turned on. He could not confirm whether the jets were armed and would not specify the altitude of the aircraft.