The Iranian government's deadly crackdown on demonstrators Sunday, when security forces fired on protesters on the Muslim holy day of Ashura -- a day on which violence of any kind is forbidden -- has raised anti-government anger to fever pitch.
"Killing Muslims on Ashura," one protester told ABC News by telephone from Tehran today, "is like crucifying Christians on Christmas."
In the wake of the deadliest protests in six months, reports said the Iranian government today arrested hundreds of protesters and began a roundup of prominent opposition figures.
In the bold demonstrations Sunday, the crowd lashed back at security forces, attacking riot police and burning their motorcycles and vans.
One video shows riot police cornered in a shop entrance, begging for forgiveness.
The demonstrations spread to several cities across the country and across wide swaths of Iranian society.
Several witnesses also describe a crowd more mixed than before, a sign the movement is expanding beyond the young, urban, educated people who have mostly led the charge.
"The crowd included people not just from one part of society, young and old, religious and secular," the same protester said. "It's clear lots of people are unhappy with the government."
As in several recent protests, participants condemned the regime, not just June's disputed presidential election.
"They think that this is the last chance for the regime," another protester told ABC News by telephone. "They think that this will be the end of the regime."
There will be more occasions in the coming days and weeks, including the funerals of Sunday's victims, for protesters to gather again.
Iranian state television reported that eight people had died in the street violence Sunday, although that has not been confirmed.
State television also reported that the nephew of opposition leader Mir Hossein Moussavi had been killed and his body confiscated in an effort to stem further protests.