Iranian riot police have clashed with thousands of opposition supporters in Tehran during a Shiite religious ceremony, Al Jazeera reported.

Al Jazeera said that despite police warnings "nearly 3,000 people had gathered on Saturday in northern Tehran, where Mohammad Khatami, the former president, was expected to deliver a speech.

Police fired tear gas and used batons to disperse the crowd, which shouted anti-government slogans.

According to Al Jazeera, the opposition supporters have gathered in an apparent attempt to revive anti-government demonstrations that followed presidential elections in June when the opposition claimed the polls had been rigged in favor of Iran's hardline leader Mahmoud Ahmadinejad.

The confrontation on Saturday came as the country marks Ashura, a 10-day period of religious ceremonies which commemorate the death of Imam Hussein, a grandson of the Prophet Mohammed who was killed and beheaded in the Battle of Karbala in 680 AD by the armies of the Sunni caliph Yazid.