Iran has moved toward harder targets in Britain, such as military sites, the head of MI5 said on Tuesday, NBC News and The Independent reported.

Ken McCallum, director general of the UK's domestic intelligence agency, gave his annual threat update at MI5's headquarters in London. He said Britain and Europe had "entered a new era of national security," NBC News reported.

McCallum said Iran's leaders have been "attempting to expand their hybrid campaign" of using criminal proxies to target opponents, Iranian media groups and Israeli sites, NBC News reported. Much of it has been aimed at British Jewish communities, he said. But this year has seen a shift toward "harder targets, like military sites," NBC News reported.

He mentioned last month's incident at RAF Fairford, a base in England used by U.S. bombers in the war against Iran. He would not give details, citing ongoing investigations, but said the case was "not unique," NBC News reported. The U.S. had pulled its bombers from the base after reports of a possible Iranian drone attack, NBC reported.

Over the past year, MI5 investigations have led to more than 50 Iran-linked arrests in Britain, McCallum said. The agency's caseload of threats from other countries has quadrupled in the past decade, The Independent reported. MI5 now spends more on countering such threats than it did during the Cold War.

"Russia remains aggressor No. 1," McCallum said, NBC News reported. He also warned that terrorists are trying to use AI. "We've caught terrorists seeking to exploit AI to improve their reconnaissance and attack methodologies," he said, The Independent reported.

What we know: MI5 says Iran is now targeting military sites in Britain and the Fairford case was not the only one.
What we don't: Details of the Fairford plot and the other cases McCallum referred to.