The US has moved long-range bombers back to their American home stations after an unspecified new threat, according to a US official, days after the British government arrested a number of individuals in connection with an alleged Iranian plot to target the UK Fairford airbase where the planes had been stationed, CNN reports.

“We can acknowledge now that all U.S. bombers that were deployed to RAF Fairford have re-deployed to their home stations in the United States,” the official told CNN. The statement did not include details on why the planes were moved.

The source familiar called the latest threat a “real world incident.”