A number of unidentified drones have been spotted over three United States Air Force bases in England over the last six days, U.S. officials said on Tuesday. "Small unmanned aerial systems were spotted in the vicinity of and over RAF Lakenheath,

The Air Force didn’t identify who was behind the incursions, but said officials determined there was no impact on residents or critical infrastructure.

The Pentagon is “actively” watching for drones over U.S. Air Force locations in the United Kingdom, following a series of unexplained sightings over the past two weeks. The sightings, which took