British counterterrorism officers have arrested eight men, including seven Iranian nationals, in connection with two separate investigations London’s Metropolitan Police said on Sunday.
In one of the cases, four Iranians and another man whose nationality has yet to be determined were detained on Saturday on suspicion of preparing a terrorist act against a single site.
“The investigation relates to a suspected plot to target a specific premises,” the police said in a statement issued early Sunday. The police added that the site was not being named “for operational reasons.”
Dominic Murphy, the head of the Metropolitan Police’s Counter Terrorism Command, said the investigation was “fast-moving” and that police were “working closely with those at the affected site to keep them updated.”
He added: “The investigation is still in its early stages and we are exploring various lines of inquiry to establish any potential motivation as well as to identify whether there may be any further risk to the public linked to this matter.”
The police said that two of the Iranian nationals were aged 29, one was 46 and the other 40. They were arrested in London and Swindon, about 80 miles west of the capital, and in Stockport and Rochdale in the northwest. The other man was arrested in the Manchester area.
In a later statement, the police said that three Iranians, aged 39, 44 and 55, were detained at separate locations in London on Saturday but that those arrests were not connected to the other investigation.
“All three men have been taken into custody and searches continue at the three addresses,” the police said. They added that the men were detained under the National Security Act 2023, which was introduced to tighten protections against hostile acts against Britain.
Yvette Cooper, the home secretary, described the arrests as “serious events that demonstrate the ongoing requirement to adapt our response to national security threats.”
She added: “The government continues to work with police and intelligence agencies to support all the action and security assessments that are needed to keep the country safe.”
Further details of the type of plots being investigated were not given.
In a speech last year, Ken McCallum, the head of MI5, Britain’s domestic security service, identified Iran was as a country of growing concern to counterterrorism police. He said that, since January 2022, the security services had responded to 20 Iranian-backed plots that posed potentially lethal threats to British citizens and residents.
Mr. McCallum cited as an example the jailing of a man last December for reconnaissance of what was then the headquarters of Iran International, a Persian-language opposition TV channel that operates from Britain.
Speaking to the BBC on Sunday, Wes Streeting, the health secretary, said that the government “will obviously keep the public updated as we can,” but added: “given these are live investigations it wouldn’t be appropriate for me to comment further.”