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.”

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.

Unidentified drones have been spotted again over three British air bases used by the U.S. Air Force, officials confirmed Tuesday. The three bases are all located within the same area of eastern England between Cambridge and Norwich,