The latest details from the LA Times:
The Basiji militiamen could be seen fanning out throughout side streets to block demonstrators trying to flee. Armored police vans to haul away protesters could be seen parked along the roadways.
But as the militiamen tried to drag away demonstrators, one witness said, protesters joined together to overpower them and rescue their comrades. The witness also said he saw some women with their headscarves pulled off being forced into police vans. Another woman taking pictures with her cellphone camera was dragged away.
The Guardian has more.