By Nic Robertson, Tim Lister and James Frater CNN

Fairford, England (CNN) — US Secretary of State Marco Rubio said “the hands of a foreign actor” were involved in the suspected terror plot targeting a UK airbase used by the US military, revealing more about the investigation than British authorities – who have faced criticism from President Donald Trump.

“What happened this weekend could have been, and was, a very serious threat,” Rubio told Fox News Monday night, adding there was “a lot more news” to come.

“It’s one that clearly involved the hands of a foreign actor, I won’t get into great detail about that yet,” he added.

Five men, who have not been identified, were arrested early Sunday close to the base at Fairford in western England, from where US B-1 bombers have been flying missions against Iran.

But the suspects, who police said are all British nationals aged between 23 and 25 from the London area, were released on bail on Monday. That prompted criticism from US President Donald Trump, who said “I wouldn’t have done that.”

Trump said the suspects “might be” connected to Iran. “I know the answer, I can be very specific, but I’d rather not say it,” he told reporters in the Oval Office.

Rubio’s comments that the case “clearly” involved a foreign actor were less equivocal, though he declined to provide details.

“I think it ties us to the reality here. We are dealing with elements in the world, and in the case of Iran for example, who have openly threatened to attack American interests globally,” he said.

Iran has strongly denied any involvement in the incident.

Rubio noted that people were “disturbed” by the news the suspects had been released, but said British authorities have been “very cooperative and on top of it.”

The release of the five suspects does not mean that the investigation is over, and all five will be subject to stringent conditions on their movements, British counter-terrorism police said Monday.

Multiple British media outlets reported via sources that no explosives were found in the back of vans the men were driving and that the group’s swift release on bail might indicate less imminent danger than initially feared. Britain’s anti-terror laws allow police to hold suspects for up to 14 days.

Residents return

The UK has yet to publicly confirm any foreign link. Downing Street said it did not have an immediate response to Trump’s comments, and directed CNN to earlier statements made by police.

Laurence Taylor, a senior counter-terrorism police officer, said in a press conference earlier Monday police were considering the incident from every possible angle, “including that this may be actively committed by proxies or individuals either knowingly or unknowingly working on behalf of a foreign state.”

UK Prime Minister Andy Burnham chaired a meeting of COBRA – a committee that handles national emergencies – later Monday.

Interior minister Shabana Mahmood said that, as of Monday afternoon local time, “the scene is now safe.” A police cordon remains around three vehicles found at the scene.

About 85 households, who were evacuated from the area on Sunday, were told by police on Monday evening that they can return to their homes.

Aerial footage on Sunday showed a bomb disposal robot roaming between the vans in woods near the base. The rear doors of two of the vans were open and large black items could be seen scattered on the ground nearby.

CNN teams nearby later heard what sounded like two controlled detonations from the direction of the village where the vans were found.

Iran denies involvement

Iran earlier denied any involvement in the incident. Its embassy in London issued a statement Monday saying it “strongly condemns the recent unfounded and malicious speculations published by some British individuals and media outlets attempting to link Iran to arrest of five suspects in the vicinity of RAF Fairford base.”

The Iranian embassy has yet to comment on Trump’s remarks.

In July, Iran’s Islamic Revolutionary Guard Corps specifically noted Fairford’s use by US bombers, warning the UK that “any base used for aggression against Iranian territory constitutes a legitimate target for our forces.”

On Sunday, Trump called the arrests “fantastic,” saying the US and the UK had the men under investigation for “a long time.”

However, UK authorities have not commented on that assertion. It’s unclear whether the five men were under surveillance before their arrival in the Fairford area in the early hours of Sunday.

In their public statements British police say they were alerted to the men’s presence near the base by local resdidents.

“Hooded and masked”

Photographs of the men – shirtless with their hands tied behind their backs – appeared in UK media Sunday.

They were initially detained under laws on possession of explosives and were later additionally arrested “on suspicion of preparation of a terrorist act,” according to a statement by counter-terrorism police.

A local resident said she came across the men when returning home on Saturday night.

“Both the driveway and the road were blocked by three white vans,” she said.

The resident, who wishes to remain anonymous, told CNN that the vans were parked in a “strange formation” about 100 meters from the base fence.

She believed there were “definitely” more than five men in the group and most had their faces covered. However, authorities have not indicated they are looking for other individuals and said Sunday the situation had been contained. CNN is reaching out to police on the discrepancy.

Some ran into the field and some towards the neighboring village, the resident said.

She called the emergency services at 1:40 a.m., according to phone records she showed CNN. Within ten or 15 minutes, armed police arrived.

“I think it was pure luck that I arrived in the village at a similar time to the vans,” the resident, a farmer, added.

UK Defence Secretary Wes Streeting said the resident had “a partial picture” of the situation, adding that the work of the police and the security services “takes place often unsung, unreported, for good reason,” he said.

Tightened security

Local people told CNN that security around the base had been tightened in recent days, with roadblocks at the entrance. But roads and lanes in the immediate area were still open.

The woman who called the police and one other local resident said that during previous conflicts, such as that against Iraq in 2003, there had been heavy security around the base. But security since the Iran conflict began has been less evident, they said.

A US Air Force spokesperson at Fairford – where the 501st Combat Support Wing is based – told CNN on Sunday: “For operational security reasons we will not discuss specific force protection measures.”

CNN’s Molly English, Lauren Kent and Lex Harvey contributed to this report.