Kathryn Armstrong
BBC News
EPA
The investigation is being led by officers from the Metropolitan Police's Counter Terrorism Command
Three Iranian men have been charged under the UK's National Security Act on suspicion of conduct likely to assist Iran.
Mostafa Sepahvand, 39, Farhad Javadi Manesh, 44, and Shapoor Qalehali Khani Noori, 55 were arrested on 3 May.
The charges against them relate to a period between 14 August 2024 and 16 February 2025, police said. All three men have been remanded in custody and are due to appear at Westminster Magistrates' Court on Saturday.
Cdr Dominic Murphy, from the Metropolitan Police's Counter Terrorism Command, says the "extremely serious" charges come following "a very complex and fast-moving investigation".
The trio have all been charged with engaging in conduct likely to assist a foreign intelligence service, which police say is Iran.
Mr Sepahvand has also been charged with carrying out surveillance, reconnaissance and open-source research, police said, intending to commit serious violence against someone in the UK.
Mr Manesh and Mr Noori, meanwhile, have also been charged with engaging in surveillance and reconnaissance, with the intention that serious violence against someone in the UK would be carried out by others.
A fourth man, 31, was arrested on 9 May as part of the investigation but was released without charge on Thursday.
They were arrested under Section 27 of the National Security Act, the Met said, which grants police the power to arrest someone without a warrant if they are reasonably suspected of being involved in "foreign power threat activity".
Cdr Murphy said detectives had been "working around the clock" since the men were arrested, and added that officers had been "in contact with the individuals directly affected".
Frank Ferguson, head of the CPS special crime and counter terrorism division, said: "It is extremely important that there should be no reporting, commentary or sharing of information online which could in any way prejudice these proceedings."
The arrest of the three men on 3 May came on the same day that five other Iranian men were detained by police as part of a separate counter-terrorism investigation.
The men - two of whom are aged 29, a 40-year-old, a 24-year-old and another aged 46 - were arrested in Swindon, west London, Stockport, Rochdale and Manchester.
One of the men was later released on bail until an unspecified date in May, while police obtained further detention orders for the others until Saturday.
Cdr Murphy previously stressed that police were not linking the two investigations.
Speaking after the initial arrests, Home Secretary Yvette Cooper said the two operations "reflect some of the biggest counter state threat and counter terrorism operations that we have seen in recent years".