CNN: Clashes erupt in Iran as night falls on election anniversary

Tehran, Iran (CNN) -- Saturday began with calm on the streets of Tehran but clashes erupted later in the day between Iran's security forces and crowds of people gathering at the key sites to mark the first anniversary of a contested presidential election.

The first clashes Saturday were reported at about 6 p.m. as uniformed riot police and plain-clothes security forces chased away growing crowds along the sidewalks of Tehran's Vali Asr Square, witnesses said.

Witnesses told CNN they saw several people struck by batons as they were running away. They said that at least three men were arrested, blindfolded, handcuffed and swept away by security officers on motorcycles.

By most accounts, the streets of Iran's capital city were remarkably quiet from Saturday morning into the afternoon.

But tensions began to rise around 4 p.m. when a large number of security forces, riot police and members of the Islamic government's voluntary Basij forces filed into major squares and intersections, including Vali Asr, Azadi Avenue, Azadi Square and Revolution Square.

Police blocked part of a road leading to Revolution Square and traffic backed up for blocks, witnesses said. Scores of Basij and other security forces were seen waiting inside several mosques and schools near major intersections.

The disputed presidential election last year sparked widespread outrage within the Islamic republic and gave rise to the Green Movement, led by opposition candidates Mir Hossein Moussavi and Mehdi Karrubi.

But the hard-line government cracked down on protesters and has steadily been tightening its grip throughout the year, according to human rights activists. It had been difficult to predict whether demonstrations would take place or how large-scale they would turn out to be.

Fearing for people's safety, the Moussavi and Karrubi canceled plans for demonstrations Saturday but some Iranians told CNN they still planned to venture out on the streets.

"There is fear," said Azadeh, a 30-year-old bank teller in Tehran, who asked to be identified by an alias for fear of her safety. "I can't say I'm not scared, but you still have to go out -- because that's what the government wants, for you to be afraid and not continue. But we have to."