British troops have been drafted in to help the United States Air Force find out who is responsible for flying drones over three bases in England.

A small number of drones were spotted overnight flying over RAF Lakenheath and RAF Mildenhall in Suffolk and RAF Feltwell in Norfolk, USAF confirmed.

Sources told the PA news agency around 60 troops have been deployed to help USAF in its investigation of the incident.

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

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

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

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

In a statement on Tuesday, a spokesperson for USAF in Europe said: “We can confirm there were sightings yesterday 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.”