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.

The drones were detected between Wednesday and Sunday, near Royal Air Force Lakenheath, Royal Air Force Mildenhall and Royal Air Force Feltwell, all three of which are in eastern England. The bases house thousands of U.S. service members, primarily Air Force personnel.

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.