The four were initially accused of "spying" on military bases but their indictments changed in October 2018 to spreading "corruption on earth" - one of the most severe charges under Iran's Islamic law. They still face other security-related charges. Three other defendants are accused of espionage and another has been charged with "conspiracy against national security", according to IRNA.

Another activist arrested last year, Kavous Seyed Emami, a 63-year-old renowned university professor with dual Iranian and Canadian citizenship, allegedly committed suicide in prison in February 2018, a fortnight after his arrest. His widow, Maryam Mombeini, left Iran for Canada last week and was reunited with her two sons after being unable to leave for months, according to Canadian officials.

In September last year, the head of Iran's environment department, Isa Kalantari, called for clarification on the fate of the activists. "We are not asking for their release or for their execution, we just want their fate to be clarified. This is part of their citizenship rights," he said.

Copyright Agence France-Presse, 2019