Tehran, Iran (CNN) -- Political conflict and public piety converged on tension-filled streets in Tehran, Iran, on Saturday. Clashes erupted between riot police and opposition protesters as hundreds of people solemnly took part in an annual Shiite Muslim observance.
A predominantly Shiite Muslim nation ruled by a Shiite theocracy, Iran remained on the edge as the holy period of Ashura reaches its climax Sunday, when widespread protests are expected to coincide with a day of mourning for a recently deceased cleric who emerged as a champion of opposition protesters.
The opposition demonstrations were the latest to erupt in the Islamic republic since the grassroots outrage over the June presidential elections, when Mahmoud Ahmadinejad won a second term as president. The election was seen as flawed and protesters took to the streets, with many killed and hurt by security forces and others arrested.
Hundreds of riot police deployed in force at every intersection quelled several protests along a 10 km stretch of Tehran on Saturday, witnesses said. Groups of demonstrators were seen moving along Imam Hussein Square in central Tehran up to Azadi Square/Freedom Square, and security forces were there to greet them.
Witnesses said security forces outnumbered protesters, and scores of forces on motorcycles charged protesters on sidewalks whenever they started chanting anti-government slogans.
Baton-wielding security forces bashed and bloodied at least three protesters, arrested at least two people and smashed the window of at least one car, witnesses said.
One witness reported clashes between security forces and protesters in the Nivaran area of northern Tehran, with dozens of security forces riding in tandem on motorcycles charging and attacking about 500 protesters. Traffic in the area was bumper-to-bumper, car horns sounded, people chanted anti-government slogans and at least one canister of tear gas was fired to disperse crowds. Piles of debris on side streets were lit, a practice occasionally used to diminish the effects of tear gas.
One opposition Web site reported that security forces beat and injured protesters and used tear gas to disperse the crowds. A witness at the demonstrations said there were a few hundred people on the streets and disputed messages on Twitter that said tens of thousands of people were on the streets of Tehran.
The activities occurred as the Ashura holy day arrives on Sunday, and hundreds of religiously faithful people took to the streets to commemorate the holy day. That's when Shiite Muslims mark the 7th century death of Imam Hussein, grandson of the Prophet Mohammed.
Hussein was killed in battle in Karbala in 680 and is regarded as a martyr. The battle that led to his death is one of the events that helped create the schism between Sunnis and Shiites, the two main Muslim religious movements.
Religious mourning during Ashura is characterized by people chanting, beating their breasts in penance, cutting themselves with daggers or swords and whipping themselves in synchronized moves.
Sunday marks a week to the day since the death of Grand Ayatollah Hussein Ali Montazeri, a key figure in the 1979 Iranian revolution. Montazeri, who went on to become one of the government's most vocal critics, died December 20.
The seventh day after a death is a traditional time for mourning in Islam, giving Iran's opposition two reasons to demonstrate on Sunday.