Britain's domestic intelligence chief used his annual threat speech in London to warn that Iran is widening its targeting in the United Kingdom beyond dissidents to harder targets, including military sites.

MI5 Director-General Sir Ken McCallum said a suspected September plot against the U.S.-run RAF Fairford base was not unique, and that the service is devoting more resources to state threats than at any point since the Cold War. He also warned that artificial intelligence is supercharging both cyber contests and extremist misuse of technology.

McCallum drew a careful line on Russia, saying interference in the 2016 referendum should not be overstated: attempted interference, he argued, is not the same as an outcome being swayed. That assessment set up a clash at Prime Minister's Questions on Wednesday, where Prime Minister Andy Burnham was challenged by Conservative leader Kemi Badenoch.

Iran, for its part, summoned the British ambassador to demand evidence for the Fairford allegation, adding a diplomatic edge to a speech meant to set out the scale of the state-threat picture facing Britain.