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British counterterrorism officers have arrested eight men, including seven Iranian nationals, in relation to two separate alleged plots, London’s Metropolitan Police said on Sunday morning.

One of the alleged plots was a planned attack on a “specific premises”, police said.

Yvette Cooper, home secretary, said the arrests were “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.”

Five of the men were detained across England on Saturday on suspicion of preparing a terrorist act against the unnamed location, the Metropolitan police said.

Four of those individuals were Iranian citizens while the nationality of the fifth was still being established, the Met said.

In another counterterrorism operation on the same day, a further three Iranian nationals were arrested in London, the Met said in a separate statement.

The head of Britain’s MI5 domestic security service, Ken McCallum, said in October that his agents and police had tackled 20 “potentially lethal” plots backed by Iran since 2022, most aimed at dissident Iranians living in Britain. 

The spy chief said at the time that MI5 had seen Iran launch “plot after plot . . . at an unprecedented scale”.

The Met said that the first operation involved five arrests in Swindon, west London, Stockport, Rochdale and Manchester with support from officers from Counter Terrorism Policing, Greater Manchester Police and Wiltshire Police.

“As part of the investigation, officers are also carrying out searches at a number of addresses in the Greater Manchester, London and Swindon areas in connection with this investigation,” it said.

The Met said police officers had been in contact with the “affected site” to provide relevant advice and support.

Commander Dominic Murphy, head of the Met’s Counter Terrorism Command, urged the public to “remain vigilant” and pass on any relevant information they might have seen or heard.

“This is a fast-moving investigation and we are working closely with those at the affected site to keep them updated,” he said.

“The investigation is still in its early stages and we are exploring various lines of enquiry to establish any potential motivation as well as to identify whether there may be any further risk to the public linked to this matter.”

In the second operation, the Met said searches were ongoing at the three addresses. The Met said this investigation was unrelated to the arrests of the five men.

The police did not disclose details of the suspected plot, citing operational reasons.