LONDON (Reuters) - Unidentified drones are still being spotted over United States Air Force (USAF) bases in England on Wednesday, a USAF spokesperson said, confirming that a fourth base had also been targeted by the week-long airspace incursions.

Small, unmanned craft were seen flying over four bases in England, the U.S. Air Force in Europe said. The Pentagon said that there had not been “any significant mission impact.”

The drones appeared at different times between Wednesday and Saturday and hovered over the Royal Air Force’s Mildenhall, Feltwell and Lakenheath bases

It comes after the US Air Force (USAF) previously confirmed that unmanned devices ranging in 'size and configuration' had been tracked over three RAF bases in Suffolk and Norfolk last week

Dozens of British troops are assisting the US Air Force after more drones were spotted flying over multiple air bases - sparking an 'operational security' response

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,

LONDON - A criminal investigation has been launched after the U.S. Air Force reported that drones were spotted flying over English military bases, a British official said Wednesday. The U.S. Air Force reported several incursions occurred in the past week at four bases where the American forces operate.