The Associated Press
By ALI AKBAR DAREINI
The protests were in response to the demonstrations being held around the world calling for the Iranian government to release opposition activists, one of the witnesses told The Associated Press.
Protesters in Vanak and Mirdamad districts chanted "death to the dictator" and "we want our vote back" before they were attacked and beaten by police.
The witnesses spoke on condition of anonymity for fear of retaliation.
As night fell, Iranians across the city gathered on their rooftops and chanted "death to the dictator" and "courageous neighbors, thank you for your support," apparently in response to the protests around the world.
While the rooftop chanting had been common feature in the immediate aftermath of the June 12 elections, it had largely disappeared in recent weeks.
The opposition says that President Mahmoud Ahmadinejad won the June 12 elections through fraud, sparking protests across the country.
Hundreds of activists have since been imprisoned in the ensuing crackdown and at least 20 have died.
Protesters across the world on Saturday called on Iran to end its clampdown on opposition activists, demanding the release of those rounded up.
Groups including Human Rights Watch and Amnesty International are backing a global day of action, with protests planned in more than 80 cities.
