British counterterrorism police released on bail a 25-year-old dual British-Iranian national arrested Thursday in Westminster on suspicion of preparing terrorist acts in the RAF Fairford investigation. Police announced the release Saturday and said searches of two properties in Westminster had concluded.

He is the sixth man arrested in the inquiry into activity near the Gloucestershire airbase, which US bombers have used for strikes on Iran. Five British men from London, aged 23 to 25, were arrested Sept. 27 and released on bail the following day with strict restrictions on their movements and contacts. Police recovered petrol from three vehicles but found no improvised explosive devices.

Investigators are examining possible foreign state involvement. Prime Minister Andy Burnham said Wednesday there were “strong indications that Iran played a part,” while stressing that the investigation remained ongoing. Iran denies involvement. Foreign Minister Abbas Araghchi rejected Burnham’s assertion, pointing to the suspects’ release on bail and saying, “You're barking up the wrong tree.”