Via the Los Angeles Times:

At one point, anti-riot police shot into the air after they roughed up a young woman and attracted the ire of protesters. A middle-aged man could be seen staggering along the sidewalk near Tehran University with blood dripping from his face.
Protesters formed into rock-throwing crowds that fought running battles with militiamen in camouflage uniforms for control of streets and intersections, witnesses said.
By nighttime, witnesses said, the unrest stretched from the side streets along Enghelab Street all the way from Azadi (Freedom) Street to Vali Asr Street, a miles-long corridor that is among the city’s most important east-west thoroughfares. There were reports that disturbances had also broken out in other parts of the city, especially key squares in the north Tehran, but they could not be immediately confirmed.
The semiofficial Fars News Agency and other news outlets reported that one person was killed and two were injured when a bomb exploded near a shrine to Ayatollah Ruhollah Khomeini, the leader of the 1979 Islamic Revolution, on the outskirts of Tehran. The report could not be verified.
Meanwhile, Mir-Hossein Mousavi, Ahmadinejad’s reformist challenger, released a letter detailing alleged offenses that took place before and after the election and demanded an annulment of the vote.
“The social consciousness and spirit of the Iranian nation will not believe this injustice and breach of the law in its historical memory,” he said.
Reuters quoted an unidentified witness as saying that Mousavi had urged his supporters to stage a nationwide strike if he was arrested.
In downtown Tehran, contingents of baton-wielding police lined the protest route, and Tehran deputy police chief Ahmad Reza Radan announced that “as of today, no form of illegal gathering to protest against the election results should take place,” according to state television. He also warned that anyone who directed protesters to gather in the streets would be liable to arrest.
Security forces said they had acted with restraint but would soon crack down harder.
“We have behaved leniently over the past few days. I think that we should restore the law more vigorously,” said Brig. Gen. Ahmad Moqqadam, a ranking police official, according to state television. “People are tired. They want to run their business. People want to come to the streets, to travel, to fly somewhere, to go to hospital, but they are stuck in traffic for hours and their rights are denied. This process is boring, disturbing and unbearable.”