The spy scandal was uncovered in the UK over the weekend.
The three suspected men appeared then, and were formally charged with having assisted a foreign intelligence agency and with planning to use violence against a British citizen, according to British media.
Iran dismisses the British process as "politically motivated" and claims that it aims to exert pressure on Iran. The Foreign Ministry in Tehran has summoned the British chargé d'affaires there to convey a protest.
On Monday, the Foreign Ministry in London then announced that Iran's ambassador is being called in.
"The British government is clear that the defense of our national security remains our top priority and Iran must be held accountable for its actions," reads a statement.
The three men's suspected criminal activity is said to have taken place between August 14, 2024, and February 16 this year. They are said to be between 39 and 55 years old. The British police's counter-terrorism unit describes the charges as "extremely serious".
