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A prominent reformist politician, Mostafa Tajzadeh, has been arrested in Iran and accused of conspiring against the country's security.
He is also accused of "publishing false information designed to disturb public opinion". A former deputy interior minister, he spent seven years in jail in 2009-2016.
He is a staunch critic of Supreme Leader Ayatollah Ali Khamenei.
Two Iranian film directors have also been arrested for a separate protest.
Mohammad Rasoulof's films have won awards at both the Cannes and Berlin film festivals. He and Mostafa Alahmad are being held on accusations of inciting unrest.
They were among an Iranian cinema group who protested after the collapse of a 10-storey building in the city of Abadan in May, which killed more than 40 people.
Their open letter called on the security forces to lay down their weapons and not suppress protests prompted by the Metropol office block collapse.
BBC Middle East Editor Sebastian Usher says the Abadan incident quickly became a rallying cry for anger against the authorities. Protests took place not just there but elsewhere in Iran, as people blamed what they saw as official corruption and negligence for the disaster.
Mr Tajzadeh, who served under former President Mohammad Khatami two decades ago, has criticised President Ebrahim Raisi and the clerical establishment.
He has long campaigned for democratic change in Iran.
Hours before his arrest, he tweeted against government tightening of the Islamic dress code for women, Fars news agency reported.