EPAFive men have been arrested on suspicion of terrorism offences as part of an investigation into a suspected plot to "target a specific premises", police said.
Four Iranian nationals - two aged 29, one aged 40 and one aged 46 - were arrested in various locations around England on Saturday as part of a "pre-planned" counter-terror operation, the Metropolitan Police said.
The nationality and age of the fifth man is still being established, it added.
The Met said it could not provide further information at this time for operational reasons, but that the premises had been made aware and was being supported by police.
It said a 29-year-old was arrested in the Swindon area, another man aged 29 was arrested in the Stockport area, a 46-year-old was arrested in west London, and a 40-year-old was arrested in the Rochdale area.
They were detained under the Terrorism Act.
A fifth man was arrested in the Manchester area under the Police and Criminal Evidence Act (Pace).
All five were arrested on suspicion of preparation of a terrorist act. They remain in police custody.
As part of the investigation, officers are carrying out searches at a number of addresses in the Greater Manchester, London and Swindon areas.
The investigation is being led by the Met's counter-terrorism command, supported by officers from Greater Manchester Police and Wiltshire Police, as well as counter-terrorism officers from across the country.
"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," said Cdr Dominic Murphy, head of the Met's counter-terrorism command.
"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."
