What we know about RAF Fairford incident and counter-terror probe
Five men have been arrested as counter-terror police lead an investigation into a major incident near the airbase.
Five men have been arrested on suspicion of explosive and terrorism offences after a major incident was declared at an airbase in the west of England.
Bomb disposal teams have been examining a number of vehicles near RAF Fairford in Gloucestershire and dozens of homes in the surrounding area have been evacuated.
Here is a summary of what we know so far.
RAF Fairford is located in the Cotswolds, about four miles (6.4km) south of the town of Fairford, which sits along the River Coln.
The base shares a long history with the American military, and has recently been used by US warplanes as a staging post for defensive strikes on Iran.
Gloucestershire Police said they received a call about "three suspicious vehicles" travelling towards RAF Fairford at 00:45 BST on Sunday.
Five men were later arrested by its officers near Whelford, a village around two miles (3.2km) south-east of the base.
A bomb disposal team was also deployed to the village to examine a number of vehicles, police said, around which a 400m (1,312ft) cordon is in place.
Aerial pictures showed a remote-controlled robot approaching two stationary white vans in a wooded area, though its use has not been confirmed by police.
Counter Terrorism Policing (CTP) is leading the investigation into the incident.
The US military said it was "working closely" with its UK counterparts "to monitor this situation, minimise impacts and ensure the safety of US personnel, their families, and the local community".
There has been large emergency service presence in the area since the early hours of Sunday, which Gloucestershire Police Temporary Chief Constable Maggie Blyth said would remain over the next few days.
Blyth told a news conference on Sunday evening that the force would continue to assist CTP and liaise with other national partners.
She also said she would leave any declaration of a "terrorist incident" to CTP.
The five men were initially detained on suspicion of committing offences under the Explosives Act.
They were then further arrested on suspicion of preparation of a terrorist act.
The men, who remain in custody, have not been named. Police have not said where they are being held.
Asked whether police were seeking other individuals in connection with the incident, Blyth said she believed the matter was "contained".
US President Donald Trump said those arrested were "looking to do big damage", adding: "We had them under view for a long time, and we got them."
BBC Your Voice has since received an image purporting to show the moment five men were arrested.
It showed detained men in Whelford, about 350m (1,148ft) from runway access at Crash Gate 6A at RAF Fairford.
The BBC has been unable to verify the original source but BBC Verify has geolocated the image and confirmed it appeared to be authentic.
Gloucestershire Police said displaced residents have been told they will not be able to return to their homes on Sunday night.
Overnight accommodation would be found by Cotswold District Council for those affected who were unable to stay with family and friends, according to Deputy Chief Executive David Stanley.
Eighty-five households were evacuated following the incident and urged to shelter at a nearby leisure centre.
Several people have told the BBC they were woken by police in the early hours of Sunday and ordered to leave.
"We just had to throw our clothes on and come. We didn't know anything," one resident, who named herself only as Jo, said.
Another resident, Jason, said: "It all happened very quickly. We just packed our stuff up and came here."
Several people in the leisure centre are still wearing their pyjamas, according to a BBC reporter there.
A unnamed resident of Whelford told the PA news agency she called police after she saw three vans "blocking the road" and a "large group of hooded and 'balaclava'd' men".
The resident said she was driving home in the early hours of Sunday morning when she saw people in the road.
"They would have seen the bright headlights," she said. "They probably thought we were the police (and) panicked."
She added: "It would appear that by doing so I just derailed whatever they were planning."
Another resident described the moment he said he saw police apprehend the suspects.
Jeff told the BBC he heard "shouting outside his front door", although he could not be sure where it came from.
He said he then looked out of his window and saw "people being held by police outside".
Prime Minister Andy Burnham said the incident was "deeply concerning" and the government would "always take every step necessary" to protect people.
His defence secretary, Wes Streeting, declined to comment on a live operation but said he had been in contact with his US counterpart, Pete Hegseth.
Asked at a fringe event at the Labour Party conference in Liverpool whether there was any Iranian involvement, he said it was "far too early to comment or speculate, and it would be irresponsible for me to do so".
RAF Fairford has been used as a forward operating location by the US Air Force (USAF) for decades.
The base was occupied by USAF Strategic Air Command during the Cold War and later the first Gulf War in 1991.
B-52 bombers were also deployed by USAF from RAF Fairford on raids to Iraq in 2003.
It was most recently used on 1 March, following a decision by former UK prime minister Sir Keir Starmer to allow the US to use UK bases - including RAF Fairford - for "defensive" strikes on Iranian capabilities.
Conflict was sparked across the Middle East after the US and Israel launched wide-ranging strikes on Iran on 28 February.
Iran responded by launching attacks on Israel and US-allied states in the Gulf.
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