The US Air Force says its security forces at RAF Lakenheath in Suffolk responded to "suspected unauthorized drone activity" on the evening of Friday 13 November. A spokesperson says no personnel, aircraft or infrastructure were affected.
The UK Ministry of Defence says the situation was resolved and it is working with the US to establish the facts. It says it will update "in due course".
Newsweek reports that air sirens were reported at Lakenheath, RAF Mildenhall and RAF Feltwell. It remains unclear how many drones were involved, who operated them or whether any were intercepted. No one has been named as responsible.
The Wall Street Journal, as relayed by The War Zone and Newsweek, reported that US bases in England had raised their alert level over an unspecified Iranian threat. It said Mildenhall and Lakenheath were at Force Protection Condition Charlie. The US Air Force declined to say whether security levels had been raised.
Flight-tracking data cited by Newsweek shows at least nine KC-135 tankers left RAF Mildenhall for Germany and Spain on Monday 9 November, and three CV-22 Ospreys moved to Lakenheath.
MP Nick Timothy said on Facebook that, after speaking to the base, he was told there was no threat to the public and the incident was resolved.
The reported Iranian threat has not been independently checked. No link between it and the drone activity has been established.