The five men arrested over the suspected bomb plot at RAF Fairford are all British nationals from London, police have said.

The men, all aged in their twenties, were arrested on suspicion of explosive and terrorism offences in Whelford, Gloucestershire, in the early hours of Sunday morning after armed police stopped three vans travelling towards the military airbase used by US bombers.

The five UK nationals, detained on suspicion of offences under the Explosives Act and preparation of a terrorist act contrary to Section 5 of the Terrorist Act, are a 24-year-old from Camden, three men aged 23, 24, and 25 from Westminster, and a 24-year-old from Wilesden.

Dozens of homes were evacuated and bomb disposal teams were called after a villager in Whelford dialled 999 when she saw three vans and a group of masked men near the base.

Counter-terror police are understood to be investigating whether Iran is linked to the suspected terror plot at the airbase.

In a statement on social media, the Iranian Embassy said it “categorically rejects and strongly condemns the recent unfounded and malicious speculations” that it had any involvement in the suspected plot.

Senior national coordinator for Counter Terrorism Policing, deputy assistant commissioner Vicki Evans, has urged people to avoid speculation as geopolitical questions were being raised.

“This is a hugely complex and large-scale operation, involving local and national policing, the MoD, and local agencies, who are working together to progress the investigation and support for the community,” she said on Monday. “I know this has been incredibly disruptive for local people, but I’d like to reassure them that our activity is in the interest of national security, but most importantly in the interest of their own safety.

“I’d also like to thank the emergency services for their response, including the armed officers who first attended the scene, not knowing what they may face.

“I am very aware of the levels of speculation about the motivation behind this incident, and the geopolitical questions that are being raised. However, I ask that at this time, Counter Terrorism Policing are given the space to work carefully and clearly.”

US president Donald Trump said that the group were “looking to do big damage”, implying they had been “under investigation” before the incident even took place.

“We had them under investigation. They were looking to ‌do big ⁠damage to our fort and working with the British worked out great … We had them under view for a long time, and we got them,” Mr Trump said.

It is understood the police operation was not intelligence-led, meaning investigators had not known about any potential plot in advance.

A villager raised the alarm to the authorities after spotting a “large group of hooded and masked men” making their way from three large vans and noticing something “highly unusual was taking place”.

Speaking to BBC Radio 4’s Today programme, the anonymous villager said she attempted to contact the Ministry of Defence police but received no response. She contacted 999 at 1.36am as she was aware that RAF Fairford had been operating at a high security level at the time.

“I think it was pure luck that I arrived in the village at a similar time to the vans,” she said. “I am absolutely staggered that it was left to me, as a member of the public, to see and report this.

“The airbase was operating a roadblock close to the entrance to the base, but not on any of the other roads. But we assumed someone would be monitoring the roads around the base perimeter and taking regular patrols in the village.

“Clearly, this was not happening, and I believe that my 999 call foiled whatever plans they had. Even more surprising that, following my call at 1.36am, the police were aware of the presence of the three vans, but didn’t evacuate the village until 6am.

“No one from the police has been in touch to ask me anything about it. I think they were hyper-focused and vigilant about the base itself, and had absolutely no regard for our village.”

Gloucestershire Constabulary said it received reports of the suspicious vehicles travelling to the base at about 12.45am on Sunday.

Wes Streeting said the member of the public who phoned police about suspicious activity near RAF Fairford has only “a partial picture” of the situation.

The defence secretary told Sky News: “Thank you to that member of the public. She has done exactly what we would hope that someone in that extraordinary situation would do.

“I’m really grateful to her – I think she acted, by her own admission, quickly and thoughtfully, and she did the right thing,” he added. “With respect, though, she does only have a partial picture.

“And that’s as far as I wish to go this morning but I do want to emphasise my thanks to the police and the security services because their work takes place often unsung, unreported, for good reason.”

The five suspects are being held under the Police and Criminal Evidence Act (Pace), and officers have been granted an initial extension until later on Monday to hold them in custody.