Several men were arrested in a village in Whelford, Gloucestershire, in the UK on suspicion of offences under the Explosives Act on Sunday.
A major incident was declared, and homes in the region were evacuated.
The army was deployed to the area.
A specialist Army bomb disposal team is examining a number of vehicles in the area, which is located close to RAF Fairford.
The British government had given the US authorisation to carry out strikes on an Iranian missile site. RAF Fairford hosts U.S. B-1B bombers used in the strikes.
The Base had raised its security after the specific threat intelligence. The British police, however, have not said whether the arrests were made in connection with the base.
"A number of properties are currently being evacuated in the Whelford area following the declaration of a major incident," Gloucestershire Constabulary said in a statement.
"It follows the arrest of several men on suspicion of offences under the Explosives Act," the force said.
"The Army's specialist explosive ordnance disposal team are currently examining a number of vehicles," it said, adding, "The local residents are being evacuated to a nearby leisure centre."
Police said the incident was contained and they were working with partners and enacting well rehearsed plans that are in place.
The force protection conditions at RAF Fairford were raised to FPCON Delta after receiving a threat to the site. The nature of the threat was not clear.
FPCON Delta is the most restrictive level of the Pentagon's force protection system. The security measures at the site significantly increased in recent days.
Around 30 emergency vehicles were spotted in the village of Fairford near the base.
