Iran is set to elect its next president on June 12 and the run-up is turning into a major showdown of street power.
Overnight, tens of thousands of people turned out in Tehran for competing rallies.
Until now, the street has belonged to hard-line President Mahmud Ahmadinejad, who is running for a second term.
His camp, used to dominating the political arena over the past four years and certain of attention from the state media, filled Tehran's largest prayer ground on June 8 for a mass denunciation of his leading challenger, reformist candidate Mir Hossein Musavi.
It hardly mattered that Ahmadinejad himself did not show up. He reportedly was unable to make his way through his crowds of supporters and left without speaking.Opposition Shows Its Strength
But if so far it's Ahmadinejad's campaign that has been able to fill prayer grounds the size of stadiums, it was the reformists who stole the spotlight on June 8.
Musavi supporters turned out in numbers not seen before to form a human chain that they claimed ran the entire length of the capital's main north-south avenue.
Musavi supporters take to the streets of Tehran.
The reformist shouted slogans against Ahmadinejad and carried placards reading "lies are forbidden."
"People are walking in the middle of the street and on the sidewalks, they openly criticize Ahmadinejad's government, we are tired of this demagogy and lies, everybody is shouting against the lies," one demonstrator told RFE/RL's Radio Farda.
The two peaceful but competing rallies blocked traffic across the city. At one point, supporters of the two camps faced off in the streets, shouting slogans and waving flags but not clashing.
Combined, the twin rallies produced some of the biggest crowds seen in Tehran since the 1979 Islamic Revolution. At that time, popular demonstrations toppled the shah in massive demonstrations of street power.
Now, with just three days to go before the June 12 election, both the conservative and reformist camps appear to hope huge displays of support will help sway the result.Challenging Ahmadinejad
Reformists believe that a large voter turnout would favor their candidates, who include former Prime Minister Musavi and former parliament speaker Mehdi Karrubi.
Both reformists are popular among city-dwellers and younger voters who fault Ahmadinejad for mismanaging the economy and squandering Iran's oil wealth. The economy continues to stagnate, with double-digit unemployment and inflation despite record-high oil prices until recent months.
The reformist supporters would like to see Iran modernize its economy and let economic growth raise incomes.
But Ahmadinejad remains highly popular among rural voters and the poor as he promises Iran's existing economy will redress disparities of wealth.
The incumbent habitually makes large financial handouts to the poor, in the tradition of Muslim charity, as he travels the country. He also emphasizes his own humble origins and expresses disdain for technocrats.
Ahmadinejad has only one conservative challenger, the former chief of the Islamic Revolution Guards Corps, Mohsen Rezai, who is not popular enough to topple him. Opponents Face Off
The prospect of reformist and conservative crowds now trying to sway voter opinions with mass shows of strength are an unexpected development in the campaign.
Iran's reformist camp was all but invisible in terms of street presence four years ago. Then Ahmadinejad swept to power with 62 percent of the vote in a runoff poll against Akbar Hashemi Rafsanjani, a more moderate conservative who allied with the reformist camp.
But with the reformists visibly back in the game now, the race is turning into an increasingly tense showdown.
Iran's supreme leader, who holds the final word in policy decisions under the constitution, warned on June 8 against any further escalation.
"I don't want to comment about people coming into the streets, but they should not turn it into confrontation or clashes between supporters of the candidates," Ayatollah Ali Khamenei said.Nuclear Tactics
The presidential election comes as Iran continues its showdown with the United Nations over its controversial nuclear program, which the West says is intended to develop nuclear weapons.
Ahmadinejad has sharply confronted the West over Iran's nuclear program and regularly denounces the United States and Israel.
His reformist challengers, who also support Iran's nuclear program, have charged him with needlessly isolating Iran.
Musavi's supporters say a more flexible presidential style is needed with critical issues, including possible talks with Washington, so long as they don't damage Iran's interests.