Eight men have been arrested in two separate counter-terrorism police investigations.

Five were arrested at various locations around England on Saturday as part of a “pre-planned” investigation into a plot to “target a specific premises”, the Metropolitan Police said.

Four – two aged 29, one aged 40 and one aged 46 – are Iranian nationals. Police said the nationality and age of the fifth was still being established.

Three other men, all Iranian, were arrested in London on Saturday as part of a separate counter-terror police investigation. Police said the two operations were not connected.

Home Secretary Yvette Cooper thanked police and security services “for the action they have taken to keep our country safe”.

She said: “These are serious events that demonstrate the ongoing requirement to adapt our response to national security threats.”

In the operation in which five men were arrested, four were detained under the Terrorism Act. The fifth man was arrested under the Police and Criminal Evidence Act (Pace).

All five were arrested on suspicion of preparation of an act of terrorism.

The men were arrested in Swindon, west London, Stockport, Rochdale and Manchester and remain in police custody.

Police said the investigation related to a suspected plot to target a “specific premises”.

The “affected site”, which it did not name, has been made aware and is being supported by police, the Met added.

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.”

In the separate operation, the Met said three men, aged 39, 44 and 55, were arrested under the National Security Act at three separate addresses in north-west London and west London and had been taken into custody while searches continued.

Police said this investigation was not connected to the arrest of the five people. (BBC: Text, Excluding Headline)