The US air force has said it responded to “suspected unauthorised drone activity” on Friday night at an RAF airbase in the east of England.
No personnel, aircraft or infrastructure were affected, the air force said.
Sirens were heard at RAF Lakenheath in Suffolk, one of several airbases in the UK used by the US military.
The force added: “We continue to work closely with our host nation counterparts to ensure the safety and security of our US service members, US and host nation civilians, contractors and all of our families.
“Protecting our shared community is a joint responsibility, and we encourage everyone to support this effort by reporting any unusual or suspicious activity to local authorities.”
A UK Ministry of Defence spokesperson said: “We are coordinating with all relevant parties regarding reports of unauthorised drone activity at RAF Lakenheath this evening. USAF security forces personnel responded to the reports and the situation is now resolved. We are working closely with them to establish the facts. We will provide updates in due course.”
The MP for West Suffolk, Nick Timothy, said the authorities at the base had told him “there is no threat to the public, and the incident is now resolved”.
He added: “Given the raised threat level, I continue to encourage everyone to report anything suspicious or out of the ordinary to the authorities.”
RAF Lakenheath said in September it was on “Charlie alert”, the second-highest threat level that can be issued by the US department of defence.
It is home to the ۴۸th fighter wing, also known as the Liberty Wing, with almost ۷,۰۰۰ active-duty personnel making it the largest US fighter operation in Europe, according to the official base website.
Earlier this year, police investigated an alleged terror plot at RAF Fairford in Gloucestershire and a trespass incident at RAF Molesworth in Cambridgeshire. Both bases are used by the US Air Force.
In the past two months the US has evacuated planes from RAF Mildenhall in Suffolk and RAF Fairford in response to suspected attacks on the bases allegedly linked to Iran.
Donald Trump said in October that “some threats” led the US to pull its bombers from Fairford.
Police said petrol but no explosives were found during searches of vans near the base in Gloucestershire.
Two men were charged by the Crown Prosecution Service over their alleged involvement in the incident.
This week, at least ۱۲ US Air Force aircraft departed the nearby RAF Mildenhall base including two Boeing Stratotanker KC-۱۳۵ refuelling aircraft, with one headed towards Germany and another seen landing at Prestwick airport near Glasgow.
Downing Street insisted earlier this week that British air bases are safe and their security is a “top priority”.
