British Prime Minister Andy Burnham said Wednesday that there are “strong indications" Iran was involved in the events that led to the arrest of five men near RAF Fairford in Gloucestershire as part of a terrorism investigation.

Speaking after the Labour Party conference in Liverpool, Burnham said he could not disclose further details while the police investigation remains underway, but confirmed that British authorities believe Iran played a role.

US Secretary of State Marco Rubio said Tuesday that Washington believed “a foreign actor" was involved in the incident Sunday night at the airbase, which has been used by US aircraft conducting missions against Iran.

“There are strong indications that Iran played a part in what happened over the weekend at RAF Fairford, but of course it remains an ongoing, complex, and serious police investigation," Burnham told BBC News. “And of course, we are working closely with our colleagues in the United States of America. So it’s ongoing."

Burnham said he had convened the government’s Cobra emergency committee while in Liverpool and insisted that authorities were fully addressing the situation. “We are on top of it in every possible way imaginable," he said.

“We will say more in due course, but we can confirm our belief that we believe Iran to have played a part," he added. Asked why he believed Iran was involved, Burnham said, “Well I can’t go into all of those details, but obviously I wouldn’t say it lightly."

The five suspects, all London residents in their 20s, were detained in the Gloucestershire countryside near RAF Fairford after a local woman reported seeing several vans and masked men while driving home.

They were initially arrested on suspicion of explosives offenses and later detained on suspicion of preparing acts of terrorism. All five were released on police bail Monday following examinations of items found in the vans and searches at addresses associated with them in London.

Asked about the US concerns, Burnham stressed that the suspects were released under strict conditions and said British officials had remained in contact with their American counterparts.

“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. We’ve been talking to counterparts in the United States all week to explain what is happening here, how things are being done. I have complete confidence in the way British security services are handling this."