Five men arrested near RAF Fairford are now being held on suspicion of preparing a terrorist act as counter-terror officers investigate three vans.
Counter Terrorism Policing has confirmed it is leading the investigation into the major incident, which began near the US airbase overnight.
The five men were initially arrested on suspicion of offences under the Explosives Act before being further arrested on suspicion of preparation of a terrorist act, contrary to Section 5 of the Terrorism Act. All five remain in police custody while enquiries continue.
Police received a call at around 12.45am today (Sunday) concerning three suspicious vehicles which appeared to be travelling towards RAF Fairford. Armed officers responded and subsequently arrested the five men in the Whelford area.
A major emergency services operation has remained in place throughout the day, with army bomb disposal specialists examining the vehicles.
A 400-metre cordon has been established and around 85 households have been evacuated as a precaution.
Counter Terrorism Policing Senior National Coordinator, Deputy Assistant Commissioner Vicki Evans, said: “We are in the early stages of an investigation, and five men remain in custody.
“As you would expect we are working closely with our partners to understand the circumstances of the incident.
“We continue to work with Gloucestershire Police to keep the community safe as we work to gather evidence from the scene.
“A 400m cordon has been put in place around the vehicles while the Army’s Explosive Ordinance Disposal unit conduct examinations.
“As a precaution, around 85 households have been evacuated whilst these examinations take place.”
Three large vans have been under examination by bomb disposal specialists, with a specialist robot also seen being deployed.
A photograph obtained by Wiltshire 999s from a local resident at around 8am shows five men surrounded by armed police near the airbase.
The men appear topless in the image, while officers can be seen removing or examining their footwear.
There remains a significant emergency services presence around RAF Fairford, involving armed police, specialist ambulance teams and fire crews.
Personnel from the Ministry of Defence Police, Gloucestershire Police, Wiltshire Police and Thames Valley Police have all been seen in the area.
RAF Fairford is operated by the US Air Force and is used to support American military operations, including deployments of strategic bombers.
Counter Terrorism Policing said its investigation remains at an early stage and officers are continuing to gather evidence from the scene.
