It's way past midnight in Tehran, but this city is not sleeping. Outside on the streets, people are honking their horns in protest and stretching their hands out of cars making peace signs — a sign of support for Mir-Hossein Mousavi, the opposition candidate apparently defeated by President Mahmoud Ahmadinejad in Iran's presidential election on Friday. (See TIME's photos of the Iranian elections and protests)

In neighborhoods across north and central Tehran, shouts of "Death to dictator!" fill the air, mostly in female voices, coming from house windows. There are also shouts of "Allah-o Akbar!" — reminiscent of the revolution — on the urging of a communique from Mousavi's office.

Some of Tehran's main streets have been turned into urban...