Iran is increasingly seeking to target military sites in Britain, MI5 Director General Ken McCallum said Tuesday, citing the suspected plot against RAF Fairford as part of a wider threat.

Speaking during his annual threat update in London, McCallum described a significant change in Iran’s ambitions. Its operations have expanded beyond targeting dissidents to include military installations, raising concerns about threats to bases used by British and allied forces.

McCallum said the suspected Fairford plot was “not unique.” He declined to discuss details of the case because the investigation remained active, but said similar incidents had occurred in Britain and elsewhere.

RAF Fairford, in Gloucestershire, has supported U.S. bombing operations against Iran. Tehran denies involvement in the suspected plot.

McCallum said investigations linked to Iran had led to more than 50 arrests in Britain over the past year. He warned that Tehran continues to use hired criminals to carry out operations, with their abilities shaping the scale and complexity of potential attacks.

Russia, meanwhile, remains “aggressor number one,” McCallum said. He accused its military and intelligence services of escalating operations against Britain and its allies while seeking to stay below the threshold that could trigger NATO’s collective defense response.

He cited a cyberattack on Polish energy infrastructure and an attempted drone attack against a cargo aircraft in Germany as examples of the threat across Europe.

The warnings reflect a growing burden on Britain’s domestic security service. McCallum said MI5’s state-threat caseload had quadrupled over the past decade, driven chiefly by activity linked to Russia, Iran and China.