A number of unidentified drones have been spotted over three airbases in Britain, the US air force has confirmed.

“Small unmanned aerial systems” were seen between 20 and 22 November over RAF Lakenheath and RAF Mildenhall, in Suffolk, and RAF Feltwell, in Norfolk.

The USAF, which uses the bases, said it was unclear at this stage whether the drones should be considered hostile.

It also declined to comment on whether any defence mechanisms were used, but said it retains “the right to protect” installations.

A spokesperson for US air forces in Europe said: “We can confirm that small unmanned aerial systems (UASs) were spotted in the vicinity of and over RAF Lakenheath, RAF Mildenhall, and RAF Feltwell between Nov 20 and 22. The number of UASs fluctuated and they ranged in size/configuration.

“The UASs were actively monitored and installation leaders determined that none of the incursions impacted base residents or critical infrastructure.

“To protect operational security, we do not discuss our specific force protection measures but retain the right to protect the installation. We continue to monitor our airspace and are working with host-nation authorities and mission partners to ensure the safety of base personnel, facilities and assets.”

A spokesperson for the British Ministry of Defence said: “We take threats seriously and maintain robust measures at defence sites. This includes counter-drone security capabilities.

“We won’t comment further on security procedures.”