British Prime Minister Andy Burnham has said there are "strong indications" that Iran played a part in a security incident at RAF Fairford, a UK airbase used by the United States military.

"There are strong indications that Iran played a part in what happened over the weekend at RAF Fairford," Burnham told reporters. He did not provide further details. Tehran has strongly denied any involvement.

Five British men were arrested in connection with the incident on Sunday. No explosives were found at the scene. The men were subsequently released on bail, a decision that has drawn public scrutiny.

It also emerged that one of the five suspects had called emergency services himself before the group was arrested.

The British government has not publicly explained the nature of the incident, and authorities have not disclosed what specific threat, if any, was posed.

US President Donald Trump openly questioned the decision to grant bail to the suspects. Speaking at the White House on Monday, Trump said: "I will tell you, I would have said, 'don't let them have bail'. I'm surprised that they released them. I wouldn't have done that."

Burnham pushed back on those concerns, insisting the men remained under tight supervision. "I think people need to understand that when it says released - that isn't as people might think. It's obviously with the strictest possible bail conditions," he said.

"The authorities have this under the strongest grip and closest control, and I can assure you of that," Burnham added.

Earlier this week, US Secretary of State Marco Rubio said the incident at RAF Fairford "clearly involves the hands of a foreign actor."

RAF Fairford, located in Gloucestershire, is a Royal Air Force base that serves as a key facility for US military operations.