The head of MI5, Ken McCallum, said on Tuesday that Iran is trying to attack military sites in the UK and that a suspected plot at RAF Fairford was "not unique".
Mr McCallum, MI5's Director General, spoke in a public speech at Thames House in London, according to the Associated Press.
He said Tehran was seeking to widen its attacks in Britain beyond its traditional targets, who are Iranians opposed to the country's authorities.
The Hill reported that Mr McCallum described the move towards "harder targets", such as military sites, as a major shift this year.
The suspected plot at RAF Fairford in Gloucestershire took place on 27 September, according to The Hill. AP said detectives were investigating a suspected terror plot against the base.
The Washington Times reported that seven men in their 20s were arrested and released on bail under investigation. No one had been reported charged.
Mr McCallum said there had been other examples of such threats, "not just in the U.K. but around the world, most particularly in Iran's own region", according to The Hill.
He also said MI5 operations had led to more than 50 Iran-linked arrests in Britain, according to a news aggregator summary of the speech.
Mr McCallum also said Russia was expanding its attacks on the UK, according to AP and the Washington Times.
The UK Prime Minister told Parliament the plot was "almost certainly" directed by Iran's Islamic Revolutionary Guard Corps (IRGC), according to a news report headline and an aggregator summary. The brief did not confirm the full wording of the statement.
The claims about Iranian direction are those of the UK government and MI5. They have not been independently established. No response from Iran had been reported.
The Hill said the plot was reported to be a potential drone attack ordered by the IRGC. That detail was not confirmed in the speech extracts reviewed.
RAF Fairford is a Royal Air Force station in Gloucestershire that hosts US forces. AP said the base was used to bomb Iran during what it called this year's war.
MI5 is the UK's domestic security service. The IRGC is Iran's elite military force, and Britain treats it as a state actor in this context.
AP said earlier attacks in Britain included arson and sabotage at Jewish sites, which Britain says were linked to Iran. The Hill described the latest shift as an escalation from lower-level attacks, such as arson and stabbings, carried out by proxies.
Mr McCallum has made similar warnings before. In 2022, he said Iran had at least 10 potential kidnap or kill plots against UK-based "enemies" since the start of that year, according to NBC News.
That speech followed a Foreign Office summons of Iran's top UK diplomat over threats to two Iran International journalists. Iran's UN mission did not immediately respond at the time.
In October 2024, he said police and MI5 had tackled 20 Iran-backed plots since 2022, according to Al Jazeera.
Iran has denied such plots in the past. That was not verified for this case.
It was not clear whether any of the seven men would be charged. Any Iranian government or embassy response, and any UK move on sanctions, had not been reported.
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