Counter-terrorism police said Monday that the five men arrested near RAF Fairford, the English air base U.S. bombers use for strikes on Iran, are all British nationals in their 20s who live in London.

The men, aged 23 to 25, were detained near the Gloucestershire village of Whelford early Sunday under the Explosives Act, then further arrested on suspicion of preparing acts of terrorism. None has been named or charged. Police obtained a custody extension Monday.

Police are still seeking a motive

Counter Terrorism Policing said three of the men live in Westminster, one in Camden and one in Willesden.

"At this time, we are working to establish the full circumstances of the activity of those arrested, their knowledge and any motivation behind this incident," the force said.

Investigators are examining whether Iran played a role. No link has been established publicly, and officials have declined to speculate.

Iran's embassy in London said Monday that it "categorically rejects and strongly condemns" what it called "unfounded and malicious speculations" linking Iran to the arrests.

Defence Secretary Wes Streeting said it was "too early to attribute background aims, motivations for these men who are under arrest." He also said: "We know that Iran and their proxies wish to do us harm."

Prime Minister Andy Burnham called the incident "deeply concerning" and urged people not to speculate.

Two accounts of the early-hours alarm

Gloucestershire Police said it received a call about "three suspicious vehicles" traveling toward the base at about 12:45 a.m. BST on Sunday.

A farmer in Whelford, about two miles southeast of the base, gave a later time for her own call. In a radio interview, she said she came home from a party to find the road blocked by three vehicles, then saw a "large group of hooded and masked men" who scattered, some into a field.

The farmer, who asked not to be named, said she rang Ministry of Defence police but got no answer, and dialed 999 at 1:36 a.m. BST. "Within 10 minutes, the village was full of armed police," she said.

Police have not publicly said whether the two times refer to separate calls.

"I believe that my 999 call foiled whatever plans they had," the farmer said, adding that "it appears someone really dropped the ball on this."

Streeting said she "did the right thing" but added: "With respect, though, she does only have a partial picture."

Suspected explosives and a 400-meter cordon

Investigators' initial assessment was that materials found in the vehicles were consistent with improvised explosive devices.

Police said Sunday that a 400-meter cordon had been placed around the vehicles and that about 85 households had been evacuated "as a precaution."

The cordon remained in place Monday, and counter-terrorism police said it would be reviewed later in the day.

Temporary Chief Constable Maggie Blyth of Gloucestershire Police, asked whether officers were looking for anyone else, said she believed the matter was "contained."

Sonia Marsh, who lives on the base perimeter, said security had been stepped up in recent weeks. "In the prior few weeks they have put heavy, very heavy, vehicles across all gates," she said, describing "very big tractors and things like that."

A U.S. Air Force spokesperson said the 501st Combat Support Wing and other UK-based wings "remain vigilant."

RAF Lakenheath said it was at alert level Charlie, the second-highest U.S. military threat level, amid reports that Fairford was at Delta, the highest.

Washington rejects Tehran's Hormuz plan

The 501st Combat Support Wing describes Fairford as U.S. Air Forces in Europe's only bomber forward operating location, and Air Force Global Strike Command B-1 and B-52 bombers have flown missions against Iran from the base. In July, Iran's Islamic Revolutionary Guard Corps warned that "any base used for aggression against Iranian territory constitutes a legitimate target for our forces."

The arrests came as Washington and Tehran traded positions over the Strait of Hormuz. On Saturday, President Donald Trump said he had rejected an Iranian plan, conveyed through Qatari mediators, to reopen the strait within seven days.

U.S. Ambassador to the United Nations Mike Waltz said Sunday that Trump turned it down because Tehran wanted sanctions lifted and frozen assets released immediately. "They were asking for everything up front with a promise that they would then talk," he said.

Iranian Foreign Minister Abbas Araghchi told U.S. television Sunday that his country was "fully prepared for the war to be resumed" and would stand firm "even if it comes to a doomsday war."

Trump says the suspects were under watch

"They were looking to do big damage to our fort, and working with the British worked out great," Trump told reporters Sunday. "We had them under view for a long time, and we got them."

Streeting called it "a proud moment" to see the president recognize British police and intelligence work. But no British official has said publicly that the men were under prior surveillance, and Streeting declined to say what was known, citing the live police investigation. "I won't go beyond that, in terms of commenting on operational security matters," he said. Public frustration over limited information, he said, was "a small price to pay."

The police operation was not intelligence-led, meaning investigators had no advance knowledge of a plot.

Deputy Assistant Commissioner Vicki Evans, the senior national coordinator for Counter Terrorism Policing, asked that police be given "the space to work carefully and clearly."

Asked about Trump's remarks, the Whelford farmer told reporters: "I think that's wonderful, but perhaps they could have kept a closer tab on them."