The head of MI5 said on Tuesday that Iran was stepping up attempts to attack harder targets in Britain, including military sites.
Sir Ken McCallum, the Director General of MI5, made the remarks in his annual threat speech at Thames House in London, according to Reuters.
Sir Ken described a "major shift this year", which he said was "Iranian ambitions to come at harder targets, like military sites". Reuters reported the same phrase in a factbox on the speech.
He referred to a suspected plot in September to attack RAF Fairford, a US-run military air base. The Washington Times reported that Sir Ken said the incident "is not unique" and that there had been other examples, not just in the UK but elsewhere.
Sir Ken said operations linked to Iran had led to more than 50 arrests in the UK over the past year. According to Reuters and CNN, many of them were aimed at Jewish communities.
He said Iran was using criminal proxies against its opponents, Iranian media organisations and Israeli interests in Britain. He added that Iran had expanded its hybrid campaign in the past year, according to the Reuters factbox.
The arrest figures and the claims about Iranian intent come from Sir Ken, the head of the UK security service. The reports reviewed did not give details of the Fairford case, including who had been arrested or charged.
Reuters said Tehran had rejected accusations of involvement in the Fairford incident and other accusations of malign activity in Britain. Reuters did not give a date or name an Iranian official, and no separate statement from the Iranian embassy or Foreign Ministry had been reported.
Sir Ken also spoke about Russia, which he called "aggressor number one", according to Reuters, the BBC and CNN. He said state threats had quadrupled in a decade and that MI5 now devoted more resource to them than it did during the Cold War.
The BBC reported that Sir Ken said MI5's terrorism and state threats operational missions were now of roughly equal scale. His remarks therefore covered both the threat from states and the threat from terrorism.
He also spoke about artificial intelligence, which he said was "supercharging the cybersecurity contest between attackers and defenders", according to the Reuters factbox.
Sir Ken has led MI5 since April 2020. The service is responsible for protecting the UK against threats to national security, including those from foreign states and from terrorism.
Reuters said British authorities had for several years accused Iran of plots and attempted assassinations against dissidents and against Israeli and Jewish targets. It said Iran had denied those accusations.
The reports reviewed did not say what would happen next in the Fairford case. No charges or court dates had been reported.
