The Russian military has been jamming some U.S. military drones operating in the skies over Syria, seriously affecting American military operations, according to four U.S. officials.

The Russians began jamming some smaller U.S. drones several weeks ago, the officials said, after a series of suspected chemical weapons attacks on civilians in rebel-held eastern Ghouta. The Russian military was concerned the U.S. military would retaliate for the attacks and began jamming the GPS systems of drones operating in the area, the officials explained…

Humphreys, an expert on the spoofing and jamming of GPS, warns this could have a significant impact on U.S. drones, causing them to malfunction or even crash. “At the very least it could cause some serious confusion” for the drone operator on the ground if the drone reports an incorrect position or is lost, he said.