Five men are accused of preparing a terrorist act near an English air base the United States is using in its war against Iran.
London's Metropolitan Police, which leads policing efforts involving potential terror incidents, said authorities received a call about three suspicious vehicles travelling near to Gloucestershire's RAF Fairford at about 12:45am on Sunday, local time.
The arrests led to the evacuation of at least 85 nearby homes at about 7am. An hour later, Gloucestershire police declared a major incident was underway.
Residents from the evacuated properties were moved to a nearby leisure centre and told they would be unable to return to their homes through the night.
"We are in the early stages of an investigation, and five men remain in custody. As you would expect, we are working closely with our partners to understand the circumstances of the incident," Deputy Assistant Commissioner Vicki Evans, the Met's Counter Terrorism Policing senior national coordinator, said in a statement.
"A 400m cordon has been put in place around the vehicles while the Army's Explosive Ordinance Disposal unit conduct examinations."
Gloucestershire police said it believed the situation had been contained and it urged residents to follow official advice while the investigation continued.
Julian Tudsbery, who has lived in Whelford for 30 years, said another resident reported seeing three "suspicious vans" in the village early on Sunday.
"There were several police, three police cars in the drive, and they said you need to evacuate, there's been a major incident, said he couldn't elaborate," he said.
The BBC also reported a resident alerted police after seeing the three vans parked alongside a road and a group of men wearing masks.
Fears of a potential explosion
The five men were initially arrested on suspicion of committing offences under the UK's Explosives Act in the Whelford area, which backs onto RAF Fairford and hosts the headquarters of the US Air Force's 501st Combat Support Wing and the 420th Air Base Squadron.
Aerial footage aired by the British Sky News appeared to show a bomb disposal robot roaming between three white trucks.
The rear doors of two of the vans were open and large black items could be seen scattered around. The robot appeared to be working toward getting access to the third truck.
Police gave no details about the nationality of the men arrested. Suspects arrested under the Terrorism Act 2000 can be detained for up to 14 days without charge, unlike the 24-hour limit for standard arrests, without an extension application.
The US embassy in London later warned Americans in the UK to be cautious and mindful of their personal security.
British Prime Minister Andy Burnham said he knew the incident would be "deeply concerning" for many people.
"The safety and security of the public is our first priority, and I want people to know that we will always take every step necessary to protect our communities and keep our country safe," he said in a post on X.
British security officials say proxies linked to Iran have been behind a string of arson and sabotage attempts in the UK and other countries, many of them targeting the Jewish community.
They have previously warned Tehran could expand its targets in the UK if conflicts in the Middle East continue.
Interception comes amid heightened tensions
The counterterror investigation comes amid heightened tensions in the UK over the potential threat posed by hostile states, such as Russia and Iran.
In March, officials said the number of national security cases involving activity by hostile states including Iran increased by 50 per cent in the six months to December 2025.
RAF Fairford has been used by American bombers for strictly limited strikes against Iranian missile sites under an agreement with former British Prime Minister Sir Keir Starmer, who voiced opposition to the war after US and Israel launched it on February 28.
Authorities are investigating a link between the Fairford arrests and Iran as one possibility.
Iran's Islamic Revolutionary Guard Corps has previously indicated a base used to attack its territory is a legitimate target.
Tristan Wilkinson, the councillor for the Cotswold district in the UK, said authorities were aware of a threat made against the base in recent weeks.
"There was a specific threat about six weeks ago from the Iranians on this base," he said.
"At the time, there was increased surveillance around the area. This is an operational base.
Following the arrests, US President Donald Trump praised the authorities involved.
"It was an amazing job," he told reporters in Chicago.
"We had them under investigation. They were looking to do big damage to our fort.
"We had them under view for a long time and we got them."
Residents 'spooked' by air base risk
George Currie, a 20-year-old university student from the market town of Cirencester, told AFP local residents did not expect much to happen in the Cotswolds.
It's just a lovely quaint area of the Cotswolds … I'm sure all the residents of Fairford are quite spooked and jumped about it," he said.
"With how important Fairford has been with the air base, I'd be quite scared to live there at the moment."
Other residents said the air base was generally quiet apart from during a major annual air show that brought visitors from several countries.
"It's no trouble at all," a dog walker told AFP.
