Five men have been arrested on suspicion of the preparation of a terrorist act, according to the Metropolitan Police.
Counter-terror officers arrested the men, four of whom are Iranian nationals, on Saturday, with all currently in police custody.
The Met said the arrests related to a "suspected plot to target a specific premises".
In an update shortly after midnight, the force said: "Officers have been in contact with the affected site to make them aware and provide relevant advice and support, but for operational reasons, we are not able to provide further information at this time."
It added officers were carrying out searches at a number of addresses in the Greater Manchester, London and Swindon areas in connection with the investigation.
It said those detained were:
• A 29-year-old man arrested in the Swindon area
• 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
• A man whose age was not confirmed arrested in the Manchester area.
Commander Dominic Murphy, head of the Met's Counter Terrorism Command, said: "This is a fast-moving investigation and we are working closely with those at the affected site to keep them updated.
"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.
"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.
"We are working closely with local officers in the areas where we have made arrests today and I'd like to thank police colleagues around the country for their ongoing support."
Terror arrests in separate investigation
Police also arrested three further Iranian nationals in London on Saturday as part of an unrelated counter terror investigation.
The suspects were detained under section 27 of the National Security Act 2023, which allows police to arrest those suspected of being "involved in foreign power threat activity".
(c) Sky News 2025: Eight arrests in connection with two separate terrorism investigations
Child sexual abuse victims 'denied justice' after compensation scheme scrapped over cost
Fourteen children arrested on suspicion of manslaughter after industrial fire in Gateshead
What VE Day was really like - 80 years on
Reform's mission to 'remoralise' young people, says party chairman
Harry's intention may have been to extend the most public olive branch, but it could cause more hurt
Lorraine Kelly says she will undergo surgery to remove ovaries
Prince Harry criticised for saying 'I don't know how much longer my father has' in TV interview
Harry wears his heart on his sleeve – but who would have expected his interview to go this far?
