New details have emerged after five men were arrested near RAF Fairford in Gloucestershire during a major security operation.
One of the five men is understood to have called 999 himself at around 00:45 BST, almost an hour before a female farmer also contacted police after seeing men wearing balaclavas.
The five men were arrested after three suspicious vehicles were spotted near Whelford, a village directly east of RAF Fairford.
The arrests initially involved suspected offences under the Explosives Act before the investigation was also considered under terrorism offences.
Police say a quantity of petrol was found during searches of the vans, but no explosive devices were discovered.
The five men were later released on police bail while the investigation continues.
Counter Terrorism Policing says officers are continuing to investigate the circumstances surrounding the incident, including why the vehicles were in the area and what the men intended to do.
Police have urged the public not to speculate about the circumstances while the investigation remains ongoing.
RAF Fairford is an important military base in Gloucestershire and is used by the United States Air Force.
The investigation continues as officers examine the vehicles, the circumstances surrounding the arrests and the possible reasons the men were in the area.