FAIRFORD, England - President Donald Trump said five men arrested near RAF Fairford had been seeking to cause 'big damage' and had been under investigation by both U.S. and British authorities before their arrests Sunday.

British counterterrorism police are investigating the five men on suspicion of preparing a terrorist act following an early-morning security operation near the military airfield in Gloucestershire.

RAF Fairford is a British Royal Air Force base that hosts U.S. Air Force personnel and has been used by American forces during military operations involving Iran.

Trump made the new comments Sunday while speaking to reporters in the United States.

He praised the arrests and said American and British authorities had been working together.

Trump said the suspects had been under surveillance for an extended period and alleged they intended to cause significant damage at the base.

The president's characterization represents a significant new assertion about what authorities may have known before the arrests.

British police have not publicly provided the same level of detail about any prior surveillance operation or identified a specific intended target inside RAF Fairford.

Five men remain in custody

Gloucestershire Constabulary said police received a call at approximately 12:45 a.m. Sunday concerning three suspicious vehicles apparently traveling toward RAF Fairford.

Armed officers responded and arrested five men in the Whelford area, close to the airfield.

The men were initially arrested on suspicion of offenses under Britain's Explosives Act.

Counter Terrorism Policing later took the lead in the investigation.

Reuters reported that the five men were subsequently being held on suspicion of preparation of a terrorist act.

Police said all five remained in custody Sunday while investigators worked to establish the full circumstances surrounding the incident.

Major incident declared

Authorities declared a major incident and established a 400-meter cordon around vehicles connected to the investigation.

The British Army's Explosive Ordnance Disposal unit was called to examine the vehicles.

Approximately 85 nearby households were advised to evacuate as a precaution.

A nearby leisure center was opened for residents who could not stay with friends or relatives.

Armed police were deployed around the area while the investigation continued.

Police later said they believed the immediate incident had been contained.

Counterterrorism investigation in early stages

Vicki Evans, senior national coordinator for Counter Terrorism Policing, said the investigation remained in its early stages.

She said officers were working closely with partner agencies to understand the circumstances surrounding the arrests.

Gloucestershire Police urged the public not to speculate while investigators examine the evidence.

Authorities have not publicly identified the five men.

Police also have not publicly announced their nationalities, affiliations or an established motive.

Possible motives remain under investigation

Reuters reported that a source familiar with the investigation said an Iranian-linked motive was considered the most likely possibility.

The source also said investigators were examining whether the incident could have involved a Russian sabotage operation or an Islamist plot.

Those possibilities have not been announced as conclusions by British police.

No organization or foreign government has been publicly identified by investigators as responsible for the suspected plot.

The five men have not been convicted of any offense, and the allegations remain under investigation.

Fairford's role in U.S. operations

RAF Fairford has strategic importance to the United States because it can support American long-range bomber operations in Europe and beyond.

The British government has authorized U.S. bombers based at Fairford to participate in operations against Iranian missile sites connected to attacks on shipping in the Strait of Hormuz, Reuters reported.

That role has made the airfield particularly sensitive during the continuing U.S.-Iran conflict.

In July, Iran's Islamic Revolutionary Guard Corps warned Britain against allowing U.S. aircraft to use British bases for attacks on Iran.

British officials responded at the time that the country's armed forces were prepared to defend the United Kingdom against threats.

Security increased at other bases

Reuters witnesses reported increased security Sunday at other British bases used by U.S. forces.

Armored vehicles and military personnel were visible at RAF Lakenheath and RAF Mildenhall in eastern England.

A U.S. Air Force spokesperson declined to discuss specific force-protection measures.

The Air Force said its units in Britain remained vigilant and would take appropriate action to protect U.S. service members, civilians, contractors and their families.

British prime minister briefed

British Prime Minister Andy Burnham was being updated on the investigation, according to the British government.

Burnham thanked police and military personnel responding to the incident and acknowledged the concern the arrests would cause residents near RAF Fairford.

The investigation remains active

Trump's comments add new information about alleged prior U.S. and British scrutiny of the suspects, but British counterterrorism authorities have not publicly confirmed the full scope or duration of that investigation.

Investigators are continuing to examine the vehicles, evidence recovered during the operation and the circumstances that led the men toward the area surrounding RAF Fairford.

No explosion or attack at the base has been reported.

Police say the immediate incident is contained, although the counterterrorism investigation continues.

Further information is expected as British authorities determine whether charges will be filed and whether investigators can establish a specific motive or intended target.