Witnesses said authorities used batons and tear gas to break up the anti-government protests, which had been called to coincide with the state-sanctioned rallies, reported the Associated Press. Members of the foreign media were only allowed to cover the state-sanctioned rallies outside the former American Embassy in the country's capital.
Iran's Revolutionary Guard Corps had warned the opposition not to try to hijack an annual anti-U.S. rally to revive protests against the clerical establishment after June's disputed presidential election, Reuters reported.
"Police clashed with hundreds of protesters. They were chanting: 'Death to dictators'. Police used batons to disperse them," a witness said. People usually chant "Death to America" and "Death to Israel" at the annual state-organized rally.
Clashes were reported in several places in Tehran's city center and in Shiraz, a city 420 miles south of the capital.
Motorcycles belonging to a military organization also prevented Mir Hossein Mousavi, the main opposition leader, from leaving his office, reported a Web site affiliated with Mousavi, called Kaleme.org, according to the Washington Post.
Mousavi has charged massive fraud in the June 12 vote in which President Mahmoud Ahmadinejad was re-elected in a landslide. Wednesday's anti-government protests were reportedly smaller than similar demonstrations staged in September.
In Washington, President Obama issued a statement describing the 444 days that 52 Americans were "unjustly held hostage" at the embassy, as setting Iran and the United States on a "path of sustained suspicion, mistrust and confrontation."
"It is time for the Iranian government to decide whether it wants to focus on the past, or whether it will make the choices that will open the door to greater opportunity, prosperity and justice for its people," he said. (Full statement)
Editor Kelly Niknejad of the Tehran Bureau, a joint project with Frontline, said most members of the opposition are seeking changes to civil liberties, while a small number want the government overturned, and are using establish dates on the Islamic calendar to voice their discontent.
"They were saying, 'Obama, Obama, you're either with us or with them.' They were saying, 'Death to the supreme leader, death to the dictator'," during the protests, she said.
Hear Niknejad's full interview here:
-- Interview by Larisa Epatko, Online NewsHour