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.