A Russian jet fighter has intercepted a US Air Force reconnaissance plane in an "unsafe and unprofessional manner" over the Baltic Sea, the Pentagon says, and CNN reported the Russian pilot did a barrel roll over the US plane.

The US Air Force RC-135 plane was flying a routine route in international airspace on Friday when it was intercepted by the Russian SU-27 fighter, the Pentagon said.

The Russian fighter came within about 30 metres of the American plane as it performed the dangerous, high-speed manoeuvre, CNN reported, citing two US defence 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.

The incident comes amid increasingly aggressive Russian military behaviour toward Western countries. Russian jets buzzed a US warship in the Baltic Sea earlier this month.

"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 behaviour," Urban said.

The United States has made formal protests in the past when the militaries of other countries have performed similar manoeuvres.