Security forces attacked and arrested pro-reform demonstrators gathering in Tehran on Sunday to mark the anniversary of the country's 2009 disputed election, Iran opposition websites reported.
"Security forces attacked the crowd with electric batons ... in the Vali-e Asr street to disperse the demonstrators," Sahamnews.org said.
Another opposition website, Kaleme.com, said "hundreds of demonstrators" were arrested by the security forces.
Other witnesses said thousands of security personnel were deployed to stop any revival of anti-government protests that followed President Mahmoud Ahmadinejad's re-election in 2009.
Opposition websites had called for a "silent rally" to mark the vote, which reformists say was rigged to secure the hardline president's win. Authorities say the election was the most legitimate since Iran's 1979 Islamic revolution.
Sahamnews also said supporters of the opposition gathered in other parts of the city.
"Shopkeepers were ordered to close down their shops ... hundreds of people have gathered in other areas of Tehran," the website said.
Opposition leaders Mirhossein Mousavi and Mehdi Karoubi, who spearheaded protests against President Mahmoud Ahmadinejad's re-election in 2009, had been placed under house arrest after calling for a rally on Feb. 14.
Two people were shot dead at the Feb. 14 rally, during which thousands of the opposition supporters took to the streets in defiance of a heavy security presence to back uprisings in Egypt and Tunisia, that toppled their leaders.
Iran, which crushed its own anti-government protests in 2009, says uprisings in the Arab world were inspired by the country's 1979 Islamic Revolution but are worried about revival of anti-government unrest.
Iranian leaders have portrayed the Arab Spring as an "Islamic awakening", while avoiding to support the popular uprising in Syria, its most important ally in the region.
Tehran has strongly condemned military deployment by Saudi Arabia to quell unrest in Bahrain. Saudi Arabia and Bahrain are both allied to the West.