“They are jamming everything their systems can reach,” an official with the Aerorozvidka, a Ukrainian agency that develops unmanned aerial vehicles and other military capabilities, told the Associated Press in a report published Friday. “We can’t say they dominate, but they hinder us greatly.”

Russia has jammed GPS receivers on drones used by Ukrainian forces used to locate and fire artillery at enemy targets, according to the report.

Christian Brose, a former aide to Senator John McCain and author of The Kill Chain, recalled a story from a Ukrainian officer who said Russians killed a commander after tricking him into returning a wireless call from his mother, according to the report.