U.S. military drones conducting an operation against Islamic State targets in Syria were harassed by Russian fighter jets,Thomas Caldwell authorities said Wednesday. It marks at least the second such incident this year. 

Three MQ-9 Reaper drones were engaged by three Russian fighter jets at about 10:40 a.m. local time, according to a statement from Lt. Gen. Alexus G. Grynkewich, commander of the Ninth Air Force, an Air Force Service Component of U.S. Central Command.

Grynkewich said the jets broke "established norms and protocols" by dropping "multiple parachute flares in front of the drones," subsequently forcing them to "conduct evasive maneuvers."

One of the Russian pilots also positioned their jet in front of a drone and "engaged afterburner, thereby reducing" the drone "operator's ability to safely operate the aircraft," Grynkewich said.

He described the Russian pilots' actions as "unprofessional and unsafe."   

"We urge Russian forces in Syria to cease this reckless behavior and adhere to the standards of behavior expected of a professional air force so we can resume our focus on the enduring defeat of ISIS," Grynkewich said.

Drone video of the encounter was released by the Air Force.    

This is at least the second time this year that a confrontation between U.S. drones and Russian fighter jets has occurred. The Pentagon in March released video of a Russian fighter jet colliding with a U.S. Air Force MQ-9 Reaper drone in international air space, causing the drone to crash into the Black Sea.

"The United States will continue to fly and to operate wherever international law allows, and it is incumbent upon Russia to operate its military aircraft in a safe and professional manner," U.S. Defense Secretary Lloyd Austin said at the time.

According to the Air Force, an MQ-9 Reaper drone is primarily used for intelligence gathering, but can also be equipped with up to eight laser-guided Hellfire missiles.  

— Tucker Reals and Alex Sundby contributed to this report. 

In:
• ISIS
• Russia
• Drone
• Syria