WASHINGTON (Reuters) - A Russian jet fighter intercepted a U.S. Air Force reconnaissance plane on Friday in an “unsafe and unprofessional manner” over the Baltic Sea, the Pentagon said, and CNN reported the Russian pilot did a barrel roll over the U.S. plane.

The U.S. Air Force RC-135 plane was flying a routine route in international airspace when it was intercepted by the Russian SU-27 fighter, the Pentagon said, in the latest in a series of similar incidents between the U.S. and Russian militaries.

The Russian fighter came within about 100 feet (30 meters) of the American plane as it performed the dangerous, high-speed maneuver, CNN reported, citing two U.S. defense officials in the Baltic Sea region.

“This unsafe and unprofessional air intercept has the potential to cause serious harm and injury to all aircrews involved,” Pentagon spokesman Commander Bill Urban said in a statement.

“More importantly, the unsafe and unprofessional actions of a single pilot have the potential to unnecessarily escalate tensions between countries,” he said.

Earlier this month, Russian jets buzzed a U.S. guided missile destroyer, the USS Donald Cook, in the Baltic Sea. A photo released by the Pentagon appears to show the Russian jet passing at an extremely low altitude over the ship’s bow.

“There have been repeated incidents over the last year where Russian military aircraft have come close enough to other air and sea traffic to raise serious safety concerns, and we are very concerned with any such behavior,” Urban said.

Russia accused the United States of intimidation by sailing the Cook close to Russia’s border in the Baltics and warned that the Russian military would respond to any future incidents.

NATO plans its biggest build-up in Eastern Europe since the Cold War to counter what the alliance considers to be a more aggressive Russia.

The Baltic states, Estonia, Latvia and Lithuania, which joined NATO in 2004, have asked the alliance for a permanent presence of battalion-sized deployments of allied troops in each of their territories. A NATO battalion typically consists of 300 to 800 troops.

Moscow denies any intention to attack the Baltic states.