Five men arrested on suspicion of preparing a terrorist act in the vicinity of a US Air Force base at RAF Fairford in Gloucestershire, England have been released on bail as the investigation continues.

Assistant Commissioner Laurence Taylor, head of National Counter-Terrorism Policing in the U.K. provided the update in London today.

Taylor says the men were travelling in three vehicles which have been examined with the help of military officials and forensic experts.

Taylor says the five suspects have been released on bail, and are subject to “stringent conditions” on their movements and contact with others.

“They absolutely remain under investigation, as we explore multiple lines of inquiry.”

Taylor says they’re investigating the incident “with every possible angle” given current geo-political events.

“Including that this may be actively committed by proxies, or individuals either knowingly, or unknowingly, working on behalf of a foreign state.”

Gloucestershire police received a call early Sunday morning about three vehicles travelling towards the air base and five men were arrested on suspicion of committing offences under the Explosives Act. There were later arrested on suspicion of preparation of a terrorist act.