The investigation into a suspected plot near a British air base used by U.S. bombers widened this week, but it still has no charges.

Counter Terrorism Policing said it arrested a 22-year-old British man on Tuesday in Westminster, London. He is held on suspicion of preparing terrorist acts under Britain's Terrorism Act. Police also searched a property in the same area.

"This remains a live investigation," said Vicki Evans, who leads counterterrorism policing nationally. She said teams are "working around the clock" to find the motive. Six other men in their 20s remain on police bail. Five were arrested on Sept. 27 and one on Oct. 1.

The case began when police stopped three suspicious vans near RAF Fairford in Gloucestershire on Sept. 27, AFP reported. Officials declared a major incident and cleared a nearby village. Investigators found no explosives in the vans, but did find some petrol, according to officials. One of the men on bail is a dual British-Iranian citizen.

The base matters to the U.S. Britain gave Washington permission in March to use Fairford for "specific defensive operations into Iran." U.S. bombers have flown from there since.

On Monday, President Donald Trump said the U.S. had moved all of its B-1 bombers out of Fairford because "there were some threats." He said: "We actually know the people that made the threat." Trump has also criticized British police for releasing the suspects on bail.

British Prime Minister Andy Burnham has said there were "strong indications that Iran played a part," AFP reported. Iran has rejected that. U.S. Secretary of State Marco Rubio has played down any specific threat.

Police are asking anyone with information to contact the Anti-Terrorist Hotline.

What we know: Seven men have been arrested, six are on bail, and no one has been charged.
What we don't: What the suspects planned, and whether Iran was behind it.