WASHINGTON » Mysterious, middle-of-the-night drone flights by the U.S. Secret Service during the next several weeks over parts of Washington are part of secret government testing intended to find ways to interfere with rogue drones or knock them out of the sky.

A U.S. official briefed on the plans tells The Associated Press that the Secret Service is testing drones for law enforcement or protection efforts and looking for ways to thwart threats from civilian drones, such as signal jamming. The drones will be flown between 1 a.m. and 4 a.m. The official spoke on condition of anonymity because this person was not authorized to publicly discuss the plans and the Secret Service said details were classified.

Some consumer-level drones are powerful enough to carry small amounts of explosives or a grenade.