Reports say that Iranian security forces have fired tear gas and clashed with opposition supporters in Tehran.
Earlier in the day, opposition supporters said they planned to hold a march in the capital to demand the release of opposition figures Mir Hossein Musavi and Mehdi Karrubi, who spearheaded protests against President Mahmud Ahmadinejad's disputed reelection in June 2009.
Iranian officials have denied reports that Musavi and Karrubi have been jailed but have not confirmed the whereabouts of the two men.
Musavi and Karrubi have been living under virtual house arrest since they called for a February 14 rally to support the uprisings in Arab countries.
Their families and opposition websites say the two men and their wives were arrested on February 17 and transferred to a jail outside Tehran.
Prosecutor General Gholam Hossein Mohseni Ejeie said that the allegations were "false."
compiled from agency reports