An Iranian opposition website said on Sunday that hundreds of security forces had deployed in central Tehran, where the opposition planned to stage fresh anti-government rallies during a Shi'ite religious festival, Reuters reported.
"Hundreds of police, riot police and security forces are at Haft-e Tir square, Enqelab Street and near the main Bazaar," the Jaras website reported.
The moderate opposition has urged people to gather in central Tehran on Sunday morning.
Baton-wielding riot police fired tear gas and warning shots on Saturday to disperse supporters of opposition leader Mirhossein Mousavi in various parts of Tehran.
In another sign that the anti-government protests in Iran were not dying down six months after a disputed June 12 presidential election, clashes also took place in another areas on Saturday, including the central city of Isfahan.
Reformist website Norooz said security forces in Isfahan clashed with mourners of late dissident cleric Grand Ayatollah Hossein Ali Montazeri who died aged 87 a week ago.
This year's religious holy day of Ashura falls on Sunday, the seventh day of mourning for Montazeri. In the Shi'ite religion, friends and family traditionally gather to commemorate the deceased a week after their death.
Asura is one of the main Shi'ite holy days, when the Shi'ite faithful commemorate the slaying of the prophet Mohammad's grandson Hussein in Kerbala in 680 AD.