The men have been arrested on suspicion of violating the Explosives Act. Military bomb experts have been called to the scene and are examining several vehicles.
"The scene is cordoned off but we believe the incident is under control," Gloucestershire Police said in a statement, according to Sky News.
It is unclear whether the incident is directly linked to the air base in the area, RAF Fairford, which is used by both the UK and the US.
The base has been used by the US in the war against Iran. Britain said in July that its military was ready to defend the country after Iran's Revolutionary Guard warned it against allowing US bombers to take off from Fairford, according to Sky News.
A US Air Force spokesman told Reuters they were aware of the details of the incident, but would not comment on any safety measures being taken.
