LONDON (Reuters) -Three Iranian men appeared in court in London on Saturday accused of offences under the National Security Act following a major counter-terrorism investigation by British police.

The three men have been charged with engaging in conduct likely to assist a foreign intelligence service between August 14, 2024, and February 16, 2025, police said, adding that the foreign state to which the charges relate is Iran.

The charges come at a time of intense scrutiny of suspected Iran-backed activities in Britain.

Interior minister Yvette Cooper said Britain would take "separate action" to address the serious issues raised by the case of the three men.

"Iran must be held to account for its actions," she said in a statement. "We must also strengthen our powers to protect our national security as we will not tolerate growing state threats on our soil."

The charges against the three men come after police arrested eight men including seven Iranians earlier in May, in two separate operations which Cooper said were some of the biggest investigations of their kind in recent years.

The three men - Mostafa Sepahvand, 39, Farhad Javadi Manesh, 44, and Shapoor Qalehali Khani Noori, 55 - were remanded in custody and will appear at a preliminary hearing at the central criminal court on June 6.

Sepahvand, whose application for bail was denied, arrived in Britain in 2016 concealed in a lorry, the court heard, while the other two men arrived by irregular means, the government said, including via small boats across the Channel.

Immigration is a major political issue in Britain, where many voters are worried over the high numbers of arrivals. Prime Minister Keir Starmer has promised to reduce the number of small boat crossings by targeting people smuggling gangs.

IRAN INTERNATIONAL

Britain's domestic spy chief Ken McCallum said last year that officers had responded since 2022 to 20 Tehran-backed plots that potentially posed lethal threats to UK citizens and residents.

The court on Saturday heard allegations that the three men had targeted Britain-based journalists connected with Iran International, a broadcaster which is critical of the Iranian government.

Sepahvand was also charged with surveillance and intending to commit serious violence against a person in Britain, while Manesh and Noori were charged with surveillance and the intention that serious violent acts would be committed by others.

Iranian Foreign Minister Abbas Araqchi has previously said he was "disturbed" to learn that Iranian citizens had been arrested by British authorities.

He said Tehran was ready to assist in investigations if "credible allegations of misconduct are established", while another foreign ministry official rejected any accusations against Iran as "baseless".

In 2023, an Austrian national was convicted of carrying out "hostile reconnaissance" against the London headquarters of Iran International. Last year a British journalist of Iranian origin who worked for Iran International was stabbed in London.

The British government has placed Iran on the highest tier of its foreign influence register, requiring Tehran to register everything it does to exert political influence in the UK.

(Reporting by Sarah Young in London and Gursimran Kaur in Bengaluru; Editing by Susan Fenton and Gareth Jones)