The blaze erupted in the early hours of Sunday inside an "old or disused building" at the RAF Fairford airbase, a UK Ministry of Defense spokesman was cited as saying by GB News.
"An investigation has been initiated and is ongoing. More information will be released as it becomes available," the Air Force said in a statement published by the channel.
No one was injured in the fire, which was contained, nor did the blaze pose any threat to the base or the local community, the authorities said.
The UK government noted in March that it had allowed the United States to use the base for strikes on Iran, but only for what it described as "defensive" operations. Demonstrators rallied outside the airbase to protest against US attacks on Iran.