British counter-terrorism police have arrested at least eight men in a major counter terrorism operation.

Five men, including four Iranian nationals, were arersted earlier on suspicion of planning a terrorist act, a statement from London’s Metropolitan Police said on Sunday.

The investigation relates to a suspected plot to target a specific location, according to the statement, which added that the men were arrested during raids at a number of addresses across the country on Saturday.

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“This is a fast-moving investigation, and we are working closely with those at the affected site to keep them updated,” said Commander Dominic Murphy, head of the Met’s Counterterrorism Command.

The Met Police have not said which site was the target of the alleged attack. It said the men were arrested in the Greater Manchester and London areas, as well as in the southern town of Swindon.

“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,” Murphy said.

Four of the men are Iranian nationals, ranging in age from 29 to 46, and have been detained under Britain’s Terrorism Act, the police statement said.

The nationality of the fifth man, whose age was not provided, was still being established and the Met statement said he had instead been detained under the Police and Criminal Evidence Act.

All five remain in police custody.

“We understand the public may be concerned and as always, I would ask them to remain vigilant and if they see or hear anything that concerns them, then to contact us,” Murphy said.

A 29-year-old man arrested in the Swindon area, while a 46-year-old man arrested in west London, a 29-year-old man arrested in the Stockport area, a 40-year-old man arrested in the Rochdale area, and a man of unknown age was arrested in the Manchester area.

Three other, unrelated, Iranian men have also been arrested.

Two of the men, aged 39 and 44, were arrested at separate addresses in northwest London on Saturday, the Metropolitan Police said.

A 55-year-old man was apprehended at a third address, in west London.

-With AAP