Five British men arrested near a U.S.-operated air base in England have been released on bail as counterterrorism police investigate whether the incident was linked to Iran.

Axar.az reports, citing AP, that the men, all British nationals in their 20s from London, were arrested Sunday near RAF Fairford in Gloucestershire after police received reports of suspicious vehicles.

The suspects were initially detained on suspicion of explosives offenses and were later arrested on suspicion of preparing an act of terrorism. Police said they were investigating multiple lines of inquiry, including possible links to Iran, Russia or non-state militant groups.

Police said the suspects face strict bail conditions and remain under investigation. Britain’s PA news agency reported that officers had not found viable explosives.

Iran has denied any involvement. The Iranian Embassy in London described speculation linking Tehran to the incident as “unfounded and malicious.”

RAF Fairford has been used by U.S. B-1 and B-52 bombers during the conflict with Iran. The U.S. Air Force said personnel at the base remain vigilant.