Prime Minister Andy Burnham says there are “strong indications” Iran “played a part” in the suspected plot near RAF Fairford in Gloucestershire.
He said the investigation remains active and praised counterterrorism officers.
Five British men in their twenties were arrested Sunday on suspicion of terrorism and explosives offenses.
Released Monday under strict bail conditions, they remain under investigation.
Police recovered gasoline from three vans but found no improvised explosive devices.
The base has been used by U.S. bombers for strikes against Iran.
Tehran has denied involvement, condemning the allegations as “unfounded and malicious speculation” linking it to the suspected plot.