Counter-terrorism police have arrested five men on suspicion of terrorism offences, the Metropolitan 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 operation”, the force said.
The nationality and age of the fifth man is still being established, it added.
The investigation relates to a “suspected plot to target a specific premises”, the Met said, adding for operational reasons it cannot provide further information at this time.
Officers have made the affected site aware and provided advice and support, police said.
The Met 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.”