The suspect, 41, who had been “entrusted with sensitive information,” was arrested on suspicion of espionage, according to U.S. and British authorities.

At least a dozen U.S. refueling planes and other aircraft departed on Monday from a British base that is a major hub for the U.S. Air Force. The reasons behind the move remain unclear.

U.S. allies are not celebrating Trump's midterm defeat, viewing the election results instead as another worrisome sign of a fickle electorate and unreliable partner.

In annual speech on threats, Ken McCallum, the head of MI5, cited a “major shift” in Tehran’s “ambitions” to attack military sites and other high-security targets.

The mixed signals expose a split in President Donald Trump’s approach to Russia, amid strain on energy markets.