Russia said it summoned a U.S. defense attache on May 23 after it claimed an American military aircraft flew into civilian airspace during a reconnaissance mission near Russia's Far Eastern border.
Russia's Defense Ministry said that the U.S. Air Force RC-135 surveillance plane risked colliding with passenger planes as it flew over the Sea of Japan on May 22 because it had turned its transponders off and could not be detected by civilian radar, although it was flying at an altitude typically used by passenger jets.
The U.S. crew did not inform regional authorities of the plane's route, the ministry said.
"The U.S. plane crew's unprofessional actions created the danger of a collision with...civilian airlines," the ministry said, adding that measures must be taken to prevent such incidents in the future.
In recent months, Washington has repeatedly accused Russian aircraft of buzzing U.S. warships and aircraft in an "unprofessional" and dangerous manner.
Moscow has countered that the U.S. military has no business getting too close to Russia's borders.