Iran on Monday arrested Ali Asghar Gharavi, the author of a controversial article seen by critics as questioning the beliefs of Shiite Islam, a prosecutor general said.
"In regards with the banned newspaper (Bahar), the author of that article was arrested yesterday," prosecutor Mohseni Ejeie was quoted as saying by Fars news agency.
In late October, the pro-reformist Bahar daily published an opinion piece penned by Gharavi, which drew heavy criticism from the authorities.
Bahar had issued an apology, saying publishing the article was an "unintentional mistake" and it had temporarily suspended activities to "ease the tensions".
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But the Iran's press watchdog banned the reformist daily and Saeed Pourazizi, the head of newspaper, was arrested on November 2 for publishing the article. He was later freed on bail.
Judiciary chief Ayatollah Sadegh Larijani has warned his department will "act with determination against those who falsify the history and try to undermine the fundamentals of the regime."
Iran's President Hassan Rouhani, a cleric and a reputed moderate, pledged to work for greater social freedoms during his election campaign.
Several reformist journalists and political activists in the majority Shiite country have been released since he took office in August.
Bahar and several other reformist dailies only resumed publication at the end of 2012 after a ban lasting several years.