British authorities said they were releasing five men on bail who were arrested over a foiled attack on an air base in England that houses U.S. forces. Officials familiar with the matter said earlier that investigators were probing whether Iran or an Islamist group had orchestrated the plot.

Police on Monday said the five men, who were arrested a few hundred yards from RAF Fairford in western England over the weekend, were all U.K. nationals in their 20s. "They absolutely remain under investigation," said Laurence Taylor, the U.K.'s head of counterterrorism policing, who added that the men's movements would be restricted.

No motive has been identified for the failed attack, though security officials suspect U.S. B-1 bombers at the base were a likely target.

Iran's Embassy in the U.K. said Monday it "categorically rejects" attempts to link Iran to the arrests, calling such reports "unfounded and malicious speculations," in a statement on X.

Images published by local outlets Sunday showed five shirtless men being arrested by counterterrorism police, while a robotic bomb-detection crew searched three white vans. Large black canisters sat nearby on the road, the images showed. The men, who all live in London, were arrested on suspicion of preparing a terrorist act.

Iran had warned the U.K. earlier this year that it would face consequences for allowing the U.S. to use its bases to attack the country. U.S. bombers have used Fairford base to fly sorties in the Middle East conflict.

American and British security officials were aware of a growing threat to the base in recent weeks. President Trump said the U.S. and U.K. had the men under investigation. Security at the base, which is one of the few military air bases in Europe with a runway long enough to launch heavy bombers, had been ramped up in recent days. Plane spotters and locals said that security around the base increased last week, with vehicles placed around the perimeter to guard against breakthroughs of the fence. There are currently a dozen B-1 bombers at the base.

Taylor said the police were "keeping an open mind" about a possible connection to geopolitical events, including "that this may be actively committed by proxies, or individuals either knowingly or unknowingly working on behalf of a foreign state."

British media reported the five men, whom police said were aged between 23 and 25, were arrested after a chance encounter by a farmer who was driving home from a party just after midnight early Sunday and spotted three white vans blocking a road a few hundred yards from the base. She then saw a group of men wearing balaclavas running to hide, it was reported. She drove away from the scene and called police.

The farmer has criticized security services for lax security around the base and for leaving residents exposed. She said her first calls to Ministry of Defense police went unanswered.

"I think it was pure luck that I arrived in the village at a similar time to the vans," she told the BBC on Monday. "I'm absolutely staggered that it was left to me, as a member of the public, to see and report this."

U.K. Defense Secretary Wes Streeting told reporters he was grateful for the woman's actions, but said she only had "a partial picture."

Both Iran and Russia have regularly used proxies-usually disaffected young local men-to carry out attacks or acts of sabotage across Europe in recent years.

This summer, the U.K. government said a series of arson and vandalism attacks on Jewish sites, including synagogues, was directed by Iran's Islamic Revolutionary Guard Corps. The attacks, which also took place across several European countries, were claimed by an Islamist group called the Islamic Movement of the Companions of the Right.

This turned out to be a front organization used by the Revolutionary Guard to target Jewish communities, the government said. The attacks were directed via young people hired online to carry out arson campaigns against targets, including the firebombing of Jewish ambulances in London.

Last year a group of pro-Palestinian activists broke into the U.K.'s biggest military air base, Brize Norton in Oxfordshire, and sprayed RAF planes with red paint.

The use of RAF Fairford has been a source of political controversy with the Trump administration. At first, the U.K. government barred the U.S. from launching bombing missions against Iran from the base, earning rebukes from Trump. The U.K. government later changed tack, allowing the U.S. to launch "defensive" sorties against Iran from U.K. military sites to protect partners across the Middle East.