Police declared a major incident following the discovery, and dozens of homes near RAF Fairford in Gloucestershire were evacuated as a precaution.

Army bomb disposal units are currently at the scene, examining the vehicles near the airbase, which is used by the United States Air Force (USAF). Counter Terrorism Policing is leading the investigation, the BBC reported.

Assistant Chief Constable Richard Ocone said in a statement: “Counter Terrorism Policing are now leading the investigation.”

“A 400m cordon has been put in place around the vehicles while the Army’s Explosive Ordnance Disposal unit examine them,” Ocone said.

“As a precaution, around 85 households have been advised to evacuate while these examinations take place,” he added.

Reacting to the development, British Prime Minister Andy Burnham described the incident as “deeply concerning”.

“I know today’s incident near RAF Fairford will be deeply concerning for local residents and for many people following developments across the country,” he said.

“I am especially grateful to those residents who have been asked to leave their homes while precautionary checks are carried out,” Burnham added.

“The safety and security of the public is our first priority, and I want people to know that we will always take every step necessary to protect our communities and keep our country safe,” the Prime Minister said.

Meanwhile, the US Department of Defense raised the threat level at RAF Lakenheath in Suffolk, which hosts the USAF’s 48th Fighter Wing, to its second-highest category, the BBC reported.

A local resident told the BBC that she alerted police to suspicious activity near the base early on Sunday.

The woman, who did not wish to be named, said she initially called Ministry of Defence (MoD) police, but nobody answered. She then called 999.

She said she had seen three parked vans and a group of men wearing masks near the area.