A small number of drones have again been spotted flying near US Air Force bases in the UK.

The US Air Force (USAF) said it was monitoring the airspace over East Anglia bases RAF Lakenheath, RAF Mildenhall and RAF Feltwell after the drones were seen overnight.

USAF said the number of sightings “fluctuated and varied between the bases” but they have not been identified as hostile.

It comes days after USAF confirmed that a small number of “unmanned aerial systems” were spotted in the vicinity of and over the three bases between Wednesday and Sunday.

UK authorities are working to ensure the safety of the sites.

USAF has not identified who is believed to be behind the incidents.

In a statement, a spokesperson for USAF in Europe said: “We can confirm there were sightings yesterday (Monday) during night-time hours and can only confirm that the number fluctuated and varied between the bases over the night.

“Since November 20, there has been no impact to residents or infrastructure and they have not been identified as hostile.

“However, they are still continuously being monitored to ensure the safety and security of the installations.”

A spokesman for the Ministry of Defence said: “We take threats seriously and maintain robust measures at defence sites.

“We are supporting the US Air Force response.”