The men were also arrested on suspicion of explosive offences in the Whelford area, outside RAF Fairford in Gloucestershire.
Five men have been arrested on suspicion of explosive and terrorism offences after they were reported travelling towards an RAF base.
Three “suspicious vehicles” travelling towards RAF Fairford in Gloucestershire were reported to police at about 12.45am on Sunday.
Five men were arrested by armed officers in the Whelford area under suspicion of committing offences under the Explosives Act.
They were then further arrested under suspicion of preparation of a terrorist act.
About 85 households have been evacuated from their homes near RAF Fairford, which is used by the United States Air Force (USAF).
A major incident was declared by police and a large emergency services presence was seen in the area, including a Hazardous Area Response Team within a 400-metre cordon.
Aerial footage showed a bomb disposal robot inspecting three white vans, two of which had open rear doors. Large black barrels appeared to be scattered around.
Counter Terrorism Policing senior national co-ordinator, 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.”
Prime Minister Andy Burnham is receiving updates on the situation.
