A military source also confirmed that the RAF had offered the US a counter-drone system that can electronically take command of an enemy drone and turn it back on itself to try to identify those flying the drones.

The US air force (USAF) said it was monitoring the airspace over the East Anglian 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.

The “Ninja” — “negation of improvised non-state joint aerial-threats” — is a counter-drone system able to identify targets up to 7km away. When the hostile drone gets closer, the system overrides the command system and sends new instructions, according to the defence firm Leonardo.

It can either force the drone to another location or back to its home base.

Ninja works with another piece of equipment called the Guardian which is known as an “electronic sniper rifle” because it can jam hostile drones from a distance of 10km. Previously this would see the drone falling from the sky and being destroyed. However, when used with Ninja the drone can be spotted early and then preserved and used for reconnaissance.

The system is known as the ORCUS counter-drone system when the two parts come together. It has previously been deployed to RAF bases where US troops are stationed, including RAF Mildenhall and RAF Lakenheath.

The new drone sightings come 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.

USAF has not identified who is believed to be behind the incidents however a UK military source said the activity could be related to something “sinister” and those behind it may be being paid to fly the drones.

They would not be drawn on whether Russia was suspected to be involved. The source said it could be a “bunch of f—wits” who were responsible, “or it could be more sinister and someone is paying them to do that”.

Security services across Europe have been on high alert for acts of arson and sabotage committed by Moscow after a spate of mysterious fires and attacks on infrastructure in the Baltics, Germany and the UK.

In October, the head of MI5, Ken McCallum, warned that Russia’s intelligence agency had been on a mission to generate “sustained mayhem on British and European streets”.

He said GRU agents had carried out “arson, sabotage and more dangerous actions conducted with increasing recklessness” in Britain after the UK backed Ukraine in its war with Russia.

In a statement, 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.”

An MoD spokesperson said: “We take threats seriously and maintain robust measures at defence sites. We are supporting the US Air Force response.”