WASHINGTON -- The U.S. is protesting an intercept of a U.S. reconnaissance plane by a Russian fighter jet last week, calling it "unsafe and unprofessional" amid what it views as increasingly aggressive air operations by Moscow.

Pentagon spokesman Mark Wright on Sunday said the U.S. was filing a complaint to Russia after the April 7 incident over the Baltic Sea.

Russian officials have denied their pilot did anything wrong, according to several news reports.

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According to the Pentagon, the U.S. RC-135U plane was flying in international airspace north of Poland. U.S. officials say a Russian SU-27 fighter intercepted the U.S. aircraft at a high rate of speed from the rear, and then proceeded to conduct two more passes using "unsafe and unprofessional maneuvers" in close proximity.

"Unprofessional air intercepts have the potential to cause harm to all aircrews involved. More importantly, the careless actions of a single pilot have the potential to escalate tensions between countries," Wright said.

"This air activity takes place in the context of a changed security environment in view of Russia's aggression against Ukraine," he said.

It isn't the first time the U.S. has protested to Moscow what it considered to be an unsafe intercept. Last April, a Russian fighter jet intercepted a U.S. reconnaissance plane in international airspace over the Sea of Okhotsk.

It's the latest incident in a recent string of international disputes involving Russian military planes.

Last month, the Swedish Air Force and NATO jets tracked four Russian combat aircraft flying with their transponders turned off over the Baltic Sea, officials said. The Russian planes - two long-range, nuclear-capable Tu-22M3 bombers and two Sukhoi Su-27 fighters - were flying in international airspace, according to Sweden's Armed Forces and alliance sources.

Also in March, the Russian military launched sweeping military maneuvers in the Arctic and other areas, a show of force ordered by President Vladimir Putin amid spiraling tensions with the West over Ukraine.

In November, Russia's military announced that its long-range bombers would conduct regular patrol missions from the Arctic Ocean to the Caribbean and the Gulf of Mexico.

Last year, a NORAD spokesperson said two F-22 fighter jets were scrambled after a pair of Russian bombers were spotted 50 miles off the coast of California.