After examination of the vehicles, authorities found no improvised explosive devices, but police said they recovered “a quantity of petrol.”

The men were later released on bail but remain under investigation. Counter Terrorism Policing are leading the investigation into any potential motivation behind the incident.

Assistant Commissioner Laurence Taylor, Head of Counter Terrorism Policing, said on Monday that “every possible angle” was being investigated, including “that this may be activity committed by proxies, or individuals either knowingly or unknowingly, working on behalf of a foreign state.”

Burnham’s comments came after U.S. Secretary of State Marco Rubio claimed that the RAF Fairford incident “clearly involves the hands of a foreign actor.”

The U.K. prime minister said that the government has been "talking to our counterparts in the United States all week to explain what is happening here, how things are being done", and that he has "complete confidence in the way British security services are handling this."

Earlier this year, the U.S. Air Force was authorized to use RAF Fairford to carry out “defensive” strikes on Iran. Iran’s Islamic Revolutionary Guard Corps (IRGC) warned the U.K. in July that any British military base used by the U.S. to launch attacks would become a “legitimate target.”