A Russian fighter jet flew “dangerously” close to a U.S. drone that was targeting Islamic State fighters over Syria Sunday morning, harassing the drone and deploying flares directly above it, Air Force officials said.

The flares damaged the MQ-9 Reaper drone’s propeller, although it was still able to land.

“The Russian fighter’s blatant disregard for flight safety detracts from our mission to ensure the enduring defeat of ISIS,” Lt. Gen. Alex Grynkewich, jead of U.S. Air Forces Central Command, said in a statement.

It’s the latest in a string of incidents involving Russian pilots harassing U.S. drones, causing tensions between the adversaries to flare up.

“We call upon the Russian forces in Syria to put an immediate end to this reckless, unprovoked, and unprofessional behavior,” Grynkewich said.