WASHINGTON — The U.S. military says it has killed three men who played key roles in developing, building and modifying Islamic State drones.

Col. Ryan Dillon, a spokesman for the U.S.-led military coalition in Baghdad, told reporters at the Pentagon Thursday that the three were killed in a series of U.S. airstrikes in Syria in mid-September.

Dillon says two of the men were responsible for manufacturing and modifying commercially produced drones. The other man was described as a drone developer, who was killed when his research workshop near Mayadin, Syria, was hit by two airstrikes.

The Islamic State group has used drones for surveillance and to fire small weapons, in both Syria and Iraq.