CAIRO  Thousands of Iranians poured into the streets of Tehran on Thursday, clapping, chanting, almost mocking the authorities as they once again turned out in large numbers in defiance of the government’s threat to crush their protests with violence.

As tear gas canisters cracked and hissed in the middle of crowds, and baton-wielding police officers chased protesters up and down sidewalks, young people, some bloodied, ran for cover, but there was an almost festive feeling on the streets of Tehran, witnesses reported in e-mail exchanges.

A young woman, her clothing covered in blood, ran up Kargar Street, paused for a moment and said, “I am not scared, because we are in this together.”

The protesters set trash afire in the street, and shopkeepers locked their gates, then let demonstrators in to escape the wrath of the police. Hotels also served as havens, letting in protesters and locking out the authorities.