The Metropolitan Police said Counter-Terrorism Policing units had arrested two men age 39 and 44 at separate addresses in north-west London on Saturday, with a 55-year-old man detained at an address in west London.
The investigation is being led by the Met’s Counter-Terrorism Command but are not connected to the arrests of five other men – four of whom were also Iranian – also carried out on Saturday, a spokesman said.
The three arrested under section 27 of the National Security Act 2023 in London remain in custody.
Section 27 grants constables the power to arrest individuals without a warrant if they reasonably suspect them of being involved in “foreign power threat activity”.
Searches continue at the three addresses across London.
Home Secretary Yvette Cooper praised Britain’s police and security forces after Saturday’s arrests.
“I want to thank the police and our security services for the action they have taken to keep our country safe.
“Protecting national security is the first duty of Government and our police and security services have our strong support in their vital work,” she told the PA news agency in a statement.
“These are serious events that demonstrate the ongoing requirement to adapt our response to national security threats.
“The Government continues to work with police and intelligence agencies to support all the action and security assessments that are needed to keep the country safe.”