Andy Burnham, the UK prime minister, said on Wednesday that “strong evidence” exists that indicates the Iranian government played a role in the weekend incident at RAF Fairford air base in western England.

Burnham, in an interview with BBC World, said: “There is strong evidence that Iran played a role in the events of the weekend at Fairford, but this case is still the subject of an ongoing, complex and serious police investigation.”

Five British men, about 20 years old, were arrested on Sunday near the base on suspicion of terrorism- and explosives-related offenses, and were later released on bail. All five are residents of London.

The incident prompted an extensive police response, and many details about it have not yet been released. U.S. forces have used the Fairford base to carry out attacks against the Islamic Republic.