The Pentagon confirmed on Sunday that all US bombers deployed to RAF Fairford had re-deployed to their home stations in the United States. A statement said "operational security precluded us from confirming the movement of our assets and forces in real-time."
The withdrawal follows a counter-terrorism investigation triggered on September 27, when a local farmer reported a group of men with several vans engaged in "suspicious" activity near the base. The scare prompted evacuations at 85 homes.
UK Prime Minister Andy Burnham said the suspected plot was likely backed by Iran but insisted the base was safe. "We have tried and tested approaches to defend our bases around the country and throughout the world," he told reporters.
US Secretary of State Marco Rubio expressed "confidence in the security of all of our bases," saying US facilities "theoretically could be threatened at any moment, and that's why there's so much security built around them." He said Washington had worked with London on the investigation and "they couldn't be more cooperative."
US bombers are not stationed permanently at RAF Fairford, the only air base on Britain's mainland used for operations into Iran. Britain gave Washington permission in March to use the base for "specific defensive operations into Iran," and some of the planes stationed there carried out recent strikes on Iran.
Iran's Revolutionary Guards said in late July the base was a legitimate target but denied involvement in any plot. Iran's embassy in London said it "categorically rejects and strongly condemns" the speculation.
Christoph Bergs, research analyst at defence think tank the Royal United Services Institute, said the redeployment would in the short term reduce the US's capacity "to quickly surge sorties against Iran, reducing the threat level somewhat."