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“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,� Lt. Gen. Alex Grynkewich, head of U.S. Air Forces Central Command, said in a statement.

Col. Michael Andrews, Air Forces Central Command spokesman, said “the Russian harassment, including close fly-bys, by one SU-34 and one SU-35 and deploying flares directly into the MQ-9, lasted almost an hour. So it wasn’t a quick fly-by, but much more of a sustained and unprofessional interaction.�

released videos of the two separate incidents that took place Wednesday and Thursday. In the first incident, which took place about 10:40 a.m. local time Wednesday in Northwest Syria, Russian SU-35 fighters closed in on a Reaper, and one of the Russian pilots moved their aircraft in front of a drone and engaged the SU-35’s afterburner, which greatly increases its speed and air pressure.

The jet blast from the afterburner can potentially damage the Reaper’s electronics, and Grynkewich said it reduced the drone operator’s ability to safely operate the aircraft.

Later a number of the so-called parachute flares moved into the drone's flight path. The flares are attached to parachutes.

In the second incident, which took place over Northwest Syria around 9:30 a.m. Thursday local time, “Russian aircraft dropped flares in front of the drones and flew dangerously close, endangering the safety of all aircraft involved,� Grynkewich said.

The drones were not armed with weapons and are commonly used for reconnaissance missions.

Army Gen. Erik Kurilla, head of U.S. Central Command, said in a statement that Russia's violation of ongoing efforts to clear the airspace over Syria "increases the risk of escalation or miscalculation.�

About 900 U.S. forces are deployed to Syria to work with the Kurdish-led Syrian Democratic Forces battling the Islamic State militants there. No other details about the drone operation were provided.