Police roadblocks and a cordon remained in place in the southwestern British village of Whelford on Tuesday morning, as the investigation continued into a possible terrorist plot near a key U.S. air base, with five men suspected of involvement arrested on Sunday but released on bail on Monday.

The men, who police said were all British nationals from London between the ages of 23 and 25, were arrested in the possession of three vans in the early hours of Sunday close to RAF Fairford, which has long been a key hub for U.S. Air Force operations in the Middle East -- including in the ongoing conflict with Iran.

Police said the men were suspected of terrorism and explosives offenses, prompting speculation that the detainees were planning to target RAF Fairford, possibly on behalf of a foreign power.

The men were bailed on Monday. Laurence Taylor, the head of National Counter Terrorism Policing in the U.K., said they were placed under "stringent conditions on their movement and contact with others." The suspects, who have not been charged, "remain under investigation as we explore multiple lines of enquiry," Taylor said.

"I know there is significant interest in whether the current geopolitical context has a bearing on this incident," Taylor said. "We are considering this from every possible angle. Including, that this may be activity committed by proxies, or individuals either knowingly or unknowingly, working on behalf of a foreign state."

Sunday's arrests, which came after a tip-off from a local farmer, were touted as a major policing and intelligence success. President Donald Trump was among those praising the operation, telling reporters on Sunday that it had been ongoing for a "long time."

Trump told reporters that the suspects were "looking to do big damage" to U.S. forces present at RAF Fairford. "The arrest in the U.K. was fantastic. Working with Britain, it was an amazing job," Trump said.

After they were bailed, Trump suggested the men "might be" linked to Iran, though declined to elaborate further.

"I'm surprised that they released them," Trump said on Monday during an Oval Office event. "I wouldn't have done that. Look, they've been very good. They worked with us very closely. We know everything about them. We would not have released them."

The Iranian embassy in London denied any connection to the incident in a statement issued on Monday. The mission condemned what it called "recent unfounded and malicious speculations published by some British individuals and media outlets."

"The circulation of such fabricated speculations, particularly in the aftermath of the criminal acts of aggression committed by the United States and the Israeli regime against the Iranian people, will serve no purpose other than to fuel Iranophobia propaganda in the UK," the embassy said.

Secretary of State Marco Rubio also suggested on Monday that the incident near RAF Fairford was linked to "a foreign actor," though said he had "to be careful" in what he shared publicly.

"There are some things I cannot say on the air for a lot of different reasons," Rubio said during an interview with Fox News. "Suffice it to say that what happened, what almost happened, what could have happened in the U.K. over the weekend is a very serious situation. It is one that clearly involves the hands of a foreign actor."

"I know a lot of people are disturbed by the news that some of these people have been released on bail," he added, thanking British authorities for their work and cooperation.

"We are dealing with elements in the world, in the case of Iran for example, who have openly threatened to attack American interests globally," he continued. "We're going to always take that very seriously, there will be repercussions for that if it ever were to happen or even attempted."

"There's a lot more news that will come out in the days to come, but there is only so much I can say right now at this point about it other than this is a very serious thing and will be responded to appropriately," Rubio said.

ABC News' Michelle Stoddart, Isabella Murray and Shannon K. Kingston contributed to this report.

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