Tehran Bureau, live-blogging along with EA, details a dramatic video:

A large poster described as bearing images of ayatollahs Khomeini and Khamenei is at the center of the action. In the first video, a man dressed in a sweater identified as a member of the Basij militia attempts to gather up the poster off the street as the crowd of protesters in the vicinity chants, "Na Ghaza! Na Lobnan! Tunis o Misr o Iran!" (Not Gaza! Not Lebanon! Tunisia and Egypt and Iran!). Suddenly, a fight breaks out and the purported Basij member is swarmed. We cannot confirm the man's membership in the militia, but this description of the event has been independently supported by @madyar via Twitter.

More from bloggers Muhammad Sahimi, Josh Shahryar, and Dan Geist:

The gates of Amir Kabir University of Technology (Tehran's Polytechnic) were shut 25BahmanMousaviStreetBlockeddown in the afternoon. It seems the authorities wanted to prevent students and faculty from joining the crowd gathering in Enghelab Avenue. An eyewitness told ourĀ  correspondent that he saw a few individuals being arrested. There were dozens of plainclothes agents among the demonstrators, most with their faces covered. ...

More on Mousavi's thwarted attempt to join the protests from Kaleme website via homylafayette: "Mousavi's bodyguards were told he could not leave [his house]. Mousavi then tried to obtain his car keys in order to drive to the protests, but was rebuffed. He and his wife, Zahra Rahnavard, then decided to leave on foot, at which point the police van was driven into the alley to seal off the exit."

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