A reformist website said Iranian riot police fired tear gas to disperse opposition supporters in Tehran who used a religious commemoration today to try to revive anti-government protests in the Islamic Republic.
"Well-equipped security forces are clashing violently with backers of the opposition in many parts of downtown Tehran," the opposition Jaras website said.
The report could not be independently confirmed, as foreign media have been
banned from covering protests.
If confirmed, the outbreak of clashes between security forces and the opposition during a two-day major Shi'ite ritual would underline escalating tension in Iran, six months after a disputed election plunged the major oil producer into turmoil.
Iranian police have warned the pro-reform opposition against staging any new demonstrations during Tasoua and Ashura on Dec 26-27, when Shi'ite Muslims mark the 7th century martyrdom of a grandson of the Prophet Mohammad.
"Police are firing tear gas to disperse a huge crowd in Imam Hossein square ... but people are resisting and chanting slogans against the government," Jaras said.
It earlier said security forces "fiercely" confronted opposition backers in different parts of the capital.
A witness said opposition supporters had gathered in groups along a several kilometres long stretch of a main downtown street. "Police aren't letting them join each other," she said.
Hardline President Mahmoud Ahmadinejad's re-election in June kindled the biggest unrest in the Islamic state's 30-year history and split the political and clerical establishment.
The authorities deny the opposition's poll rigging charges and have portrayed the huge protests that erupted after the poll as a foreign-backed bid to topple the Islamic establishment, accusing leading reformers of fomenting post-election violence.
Despite scores of arrests and security crackdowns, opposition protests have
repeatedly flared up since the vote.