Simmering tensions between Tehran and London are threatening to boil over after each country summoned the other's senior diplomats on May 19 over the charging of three Iranians with aiding a foreign spy agency to carry out activities on British territory.
The three men, all London residents, were arrested on May 3 and charged on May 17.
Iranian media on May 19 said the UK charge d'affaires in Tehran was summoned to offer an explanation for the arrests and "the baseless accusations" made against the Islamic republic.
Hours later, Britain said it summoned the Iranian ambassador to London "in response to three Iranian nationals charged under the National Security Act."
British counterterrorism authorities over the weekend charged Mostafa Sepahvand, 39, Farhad Javadi Manesh, 44, and Shapoor Qalehali Khani Noori, 55, with "engaging in conduct likely to assist a foreign intelligence service" between August 14, 2024, and February 16, 2025.
Police said the foreign intelligence service in question was Iran's.
During the initial court appearance, prosecutors alleged the three men had targeted Britain-based journalists connected with Iran International, a broadcaster that is critical of the Iranian government.
The charges came after police arrested eight men -- including seven Iranians -- in early May in two separate operations that Cooper said were some of the biggest investigations of their type in recent years.
Later on May 17, in a separate statement, police said four other men arrested as part of that operation had been released from custody but that the investigation was still open. The eighth suspect was released on May 15 without charges.
Relations between Tehran and London have worsened in recent months after a British couple traveling in Iran were charged with espionage in February.
The couple, Craig and Lindsay Foreman, had reportedly been on a world motorcycle trip when they were arrested in Iran.
British media say they entered Iran on December 30 via Armenia and intended to leave the country via the Pakistani border after five days. They had stayed in Tabriz, Tehran, and Isfahan but never checked into their hotel in Kerman.
The British government, which currently advises its citizens against all travel to Iran citing "significant risk" of arrest, questioning, or detention, has expressed "deep concern" over the charges and says it is actively seeking the couple's return.
Iran is accused by human rights groups of engaging in "hostage diplomacy," taking foreign and dual nationals for leverage in dealings with the West.