The incident on Thursday occurred when a Russian jet “performed erratic and aggressive maneuvers” as it flew within 50 feet of the U.S. aircraft’s wing tip, Danny Hernandez, a spokesman for European Command, said in a response to a question from CNN.

The Russian SU-27 began the barrel roll from the left side of the U.S. RC-135 and went over the top of it to end on the right side of the aircraft, European Command said.

The U.S. RC-135 aircraft was “intercepted by a Russian SU-27 in an unsafe and unprofessional manner,” Hernandez said, adding that the U.S. plane never entered Russian territory.

“The unsafe and unprofessional actions of a single pilot have the potential to unnecessarily escalated tensions between countries,” said Hernandez, who added that the U.S. is protesting the incident with the Russian government.