The Russian navy said it “expelled” a U.S. submarine that entered Russian waters Saturday, local media reports said. The Russian Northern Fleet’s anti-submarine force detected and drove out what it presumed to be a U.S. Navy Virginia-class vessel in the Barents Sea, an unnamed spokesman for the Russian navy told the press.

A U.S. defense official told Reuters on condition of anonymity he could not confirm the incident and would not comment to the news agency about the Russian claim. said the Pentagon did not immediately confirm the news to Fox reporters.

"An anti-submarine attack group and an Ilyushin Il-38 anti-submarine aircraft were sent to the said area to search and track the sub," the Russian navy spokesman was quoted by Interfax news agency as saying, according to Reuters. "The Northern Fleet anti-submarine forces' active maneuvers expelled the submarine from the Russian Federation's boundary waters."

The report comes as tensions between Moscow and Washington mount because of the situation in Ukraine.

Russia itself was accused of aggression Saturday. Ukrainian officials said their troops stopped a column of Russian soldiers posing as “peacekeepers” and attempting to cross the border with a humanitarian convoy. Russia denied Ukraine’s claims, which a foreign official called “fairy tales,” Reuters reported separately.