On Thursday, the harassment of the American drones continued, this time by two Russian fighter jets. The Air Force spokesman said the incident lasted for almost an hour. The Russian fighter jets have been accused of harassing U.S. hunter-killer drones twice while operating over Syria, according to the U.S. military.

In response, Lt. Gen. Alexus Grynkewich, the commander of the Ninth Air Force and the Combined Forces Air Component for Central Command, said the actions of the Russian air forces are “unprofessional and unsafe,” and urged them to cease such reckless behavior.

The incidents began on Wednesday morning, when three Reaper drones were conducting a mission against Islamic State targets in Syria. At that time, three Russian fighter jets flew close to the drones and dropped multiple parachute flares in front of them, forcing the drones to take evasive maneuvers.

The harassment continued on Thursday, when two Russian planes flew close to U.S. MQ-9 Reaper drones and dropped flares in front of them for almost an hour. In addition to the harassment of American drones, Russian and Syrian air forces have been conducting joint air defense exercises since Wednesday.

U.S. defense personnel have expressed concern that these exercises could further endanger the safety of American and Russian personnel in the region. Grynkewich warned that such unprofessional and unsafe actions by Russian air forces put the safety of Coalition and Russian forces at risk, and urged them to adhere to the standards of behavior expected of a professional air force.

He also stressed that the success of the mission against ISIS depends on the responsible conduct of all forces operating in the region.