TEHRAN — It's 4.30 a.m. in North Tehran's Tajrish Square and the sky is turning gray as dawn approaches.
President Mahmoud Ahmadinejad's supporters are out in force, celebrating. Fifty cars have gathered in the middle of the square honking horns and shouting slogans. As young men set off fireworks, the president's supporters dance alongside them. Immediately, police cars with sirens flashing, and plain-clothes policemen in unmarked Kia cars holding walkie-talkies, converge on the scene to ensure the jubilation does not get out of hand.
"We had 16 years where nothing changed, but Iran has moved in these past four years," said Esmat Mostafavi, 43, a teacher holding an Ahmadinejad poster standing outside her car along Tehran's main Vali Asr highway. "The only person who made progress on this was our president."
Later in the morning, the uptown commercial district of Tajrish starts bustling. The busy arcades are humming with fashionably dressed young people and their parents window-shopping, bargaining and flirting. News is making the rounds that Ahmadinejad is ahead in the vote count.
"I still can't believe it," says one young man into his cellphone.
Two teenagers sit behind the till at a money-changer's. In a sign that the black market is getting ever more entrenched, they have written their prices on a whiteboard and festooned the store with dollar and euro notes.
A pro-Mousavi Iranian journalist calls me to ask what's going on. For some reason, Iranians attribute divine powers to foreigners.
"I have no idea," I reply.
"So it's all over?" he whines into the phone.
The authorities have disabled sending of SMS messages and several reformist sites but Facebook is still available.
Messages and status alerts from pro-Mousavi supporters have flooded my account.
Mousavi will be holding a press conference at 2 p.m. at the reformist Etelaat newspaper and is planning to march up to the Interior Ministry with his supporters, potentially providing a flashpoint.
"We have to resist this event online," writes an Iranian user from Holland. "Facebook showed its power once already, we have to shout through it. Every Iranian must become their own media outlet."
Another member posted a report that renowned Iranian film director Mohsen Makhbalbaf claimed that the state carried out a coup d'etat on a "Mousavi government."
"If Mousavi remains silent, that will be his second betrayal of us," writes another user, a prominent Iranian feminist.
The Iranian authorities only recently allowed Facebook unfiltered, after blocking it for several years, arguing that it would be used by anti-government activists to organize online and spread dissent.
I headed down towards downtown Tehran along Vali Asr Avenue, the longest street in the Middle East, built by the Pahlavi dynasty and connects North Tehran's chic neighbourhoods to the poverty-stricken pro-Ahmadinejad strongholds of the south.
Close to the midpoint of the avenue, on Vali Asr Square, groups of protesters clustered on the edges of the square as dozens more clustered on balconies, rooftops and office windows watching the sight below.
Other central squares resounded to slogans such as "Mousavi we will protect you," and "Death to the Dictator" in a reference to President Ahmadinejad. Police dispersed protesters with tear-gas and baton-charges.
Earlier in the day, police units had used cement barriers to block the roads around the Ministry of Interior where vote counting was ongoing. Motorcycle-mounted policemen circulated among crowds shouting pro-Mousavi slogans in central Tehran.
A photographer outside Etelaat offices, where reformist candidate Mousavi was scheduled to give a press conference, reported that police had attacked journalists gathered outside. The press conference was canceled and rumors had it that Mousavi was either under house arrest or in closed talks with Supreme Leader Ali Khamenei.
"The scale of this theft has bared the real face of the Islamic Republic," said Reza Maleknasr, a protester walking through the streets of central Tehran.
(Iason Athanasiadis is reporting from Iran on a grant from the Pulitzer Center on Crisis Reporting.)
More coverage of the Iranian election:
Iran's elections: The view from the highway
Young, Iranian and ready for change
Seven visas: Reporting from Iran