U.S. troops in Europe reported a swarm of unidentified drones flying over several Air Force bases in the U.K. in the past week, a sighting that comes amid a growing mystery of UFO sightings near military installations.

It is not ruled out that Russia may be behind it. The sightings began when London authorized Ukraine to use ballistic missiles on Russian soil. Sixty electronic warfare specialists from the Royal Air Force (RAF) have been sent to the American bases on British soil due to the suspicious presence of drones near the military facilities since last week.

Unidentified drones have been spotted over U.S. bases in the United Kingdom used by American forces for a week, Fox News has confirmed.

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.

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,

Mysterious drones have been spotted flying near US Navy Bases in the UK - shortly after appliances were seen tailing a Royal Navy aircraft carrier.

Over the last few weeks, a number of drones have mysteriously been spotted over three air bases used by the US Air Force (USAF) in the UK.

The U.S. Air Force did not specify whom it believed was responsible for the drone incursion or what the perpetrator’s motivations were to carry out the operation.

Tuesday's ongoing incident occurred just days after drones were spotted near RAF Lakenheath, RAF Mildenhall, and RAF Feltwell.

British military expertise has been brought in to help find those responsible for flying drones near US military bases. About 60 RAF personnel have been sent to assist the US Air Force in its investigation,