(CNN) - US Secretary of State Marco Rubio said that "the hands of a foreign party" were involved in the suspected terrorist plot that targeted a British air base used by the US military, revealing details about the investigation beyond what was announced by the British authorities, who faced criticism from US President Donald Trump.
Rubio told Fox News on Monday evening that what happened over the weekend was - and could be considered - a very serious threat, adding that there was "a lot of news" that would emerge later.
He added: "It is a case that clearly involved the hands of a foreign actor, and I will not go into much detail about that at the present time."
Five men - whose identities were not revealed - were arrested early Sunday near the Fairford base in western England, the base from which US B-1 bombers fly to carry out missions against Iran.
However, the suspects - who police said were all British citizens between the ages of 23 and 25 and from the London area - were released on bail on Monday. This sparked criticism from US President Donald Trump, who said: "I wouldn't do that."
Trump said the suspects "may be" linked to Iran. "I know the answer, and I can be very specific, but I prefer not to say it," he told reporters in the Oval Office.
Rubio's comments - that the case "clearly" involves a foreign party - were less ambiguous, although he declined to provide details.
He said: "I think that connects us to the reality here; we are dealing with parties in the world - like Iran, for example - that have publicly threatened to attack American interests globally."
Iran strongly denied any involvement in the incident.
Rubio indicated feeling "disturbed" by news of the suspects' release, but said the British authorities had been "very cooperative and following the matter closely."
British counter-terrorism police said on Monday that the release of the five suspects does not mean the end of the investigation, and that they will all be subject to strict restrictions on their movements.
Multiple British media outlets, citing sources, reported that no explosives were found in the back of the pickup trucks the men were driving, and that the quick release of the group on bail may indicate that the danger was not as imminent as initially feared. Britain's anti-terrorism laws allow police to detain suspects for up to 14 days.
The UK has not yet publicly confirmed any foreign connection. Downing Street stated that it had no immediate response to Trump's comments, and referred CNN to previous statements made by the police.
Lawrence Taylor, a senior counter-terrorism police official, said during a press conference earlier Monday that police were examining the incident from all possible angles, “including the possibility that it was actually committed by agents or individuals working - whether knowingly or unknowingly - on behalf of a foreign state.”
British Prime Minister Andy Burnham chaired a meeting of the Cobra Committee - the committee responsible for dealing with national emergencies - later on Monday.
Interior Minister Shabana Mahmood said that, by Monday afternoon local time, “the site is now secure.” There is still a police cordon around three vehicles found at the site.
On Monday evening, police informed about 85 families - who had been evacuated from the area on Sunday - that they could return to their homes.
On Sunday, aerial footage showed a bomb-handling robot moving between pickup trucks in a wooded area near the base. The back doors of two of those trucks were open, and large black items were seen scattered on the ground nearby.
Nearby CNN teams later heard what sounded like two controlled explosions from the direction of the village where the trucks were found.
Iran had previously denied any involvement in the incident. Its embassy in London issued a statement on Monday in which it expressed its “strong condemnation of the recent speculation - which is baseless and in bad faith - spread by some British figures and media in an attempt to link Iran to the arrest of five suspects in the vicinity of the RAF Fairford air base.”
The Iranian embassy has not yet commented on Trump's statements.
In July, Iran's Islamic Revolutionary Guard Corps specifically pointed to the use of Fairford by US bombers, warning the UK that "any base used to launch aggression on Iranian territory is a legitimate target for our forces."
On Sunday, Trump described the arrests as “wonderful,” noting that the United States and the United Kingdom had been subjecting these men to investigation for a “long time.”
However, the British authorities did not comment on this allegation. It is not clear whether the five men were under surveillance before arriving in the Fairford area in the early hours of Sunday.
British police say in their public statements that they received a report from local residents about the presence of the men near the base.
On Sunday, pictures of bare-chested men with their hands tied behind their backs appeared in the British media.
They were initially detained under laws relating to the possession of explosives, but were later arrested on an additional charge of “suspicion of preparing a terrorist act”, according to a statement issued by counter-terrorism police.
A local resident said she encountered the men while returning home on Saturday night.
“Both the driveway and the road were blocked by three white pickup trucks,” she said.
A resident - who preferred to remain anonymous - told CNN that the pickup trucks were parked in a "strange formation" about 100 meters from the base's fence.
She believed the group "definitely" included more than five men, and that most of them were covering their faces. However, the authorities did not indicate that they were looking for other people, and stated on Sunday that the situation had been brought under control. CNN is contacting police to inquire about this discrepancy.
Another resident said that some of them ran towards the field, and others towards the neighboring village.
She called emergency services at 1:40 a.m., according to call logs shared with CNN. Within ten or 15 minutes, the police arrived.
British Defense Secretary Wes Streeting said one resident had a "partial picture" of the situation, adding that the work of the police and security services "often goes without praise or media coverage, and for good reason."
Local residents told CNN that security measures around the base had been tightened in recent days, with checkpoints set up at the entrance, but roads and paths in the immediate vicinity remained open.
The woman who contacted the police and another local resident stated that during previous conflicts - such as the conflict against Iraq in 2003 - there were extensive security measures around the base, but the security presence seemed less visible since the conflict with Iran began.
A US Air Force spokesman 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.”
