Hundreds of thousands of people marched in silence through central Tehran on Monday to protest Iran's disputed presidential election in an extraordinary show of defiance from a broad cross section of society, even as the nation's supreme leader called for a formal review of results he had endorsed two days earlier.
Having mustered the largest antigovernment demonstrations since the 1979 revolution, and defying an official ban, protesters began to sense the prospect — however slight at the moment — that the leadership's firm backing of President Mahmoud Ahmadinejad had wavered.
The massive outpouring was mostly peaceful. But violence erupted after dark when protesters surrounded and attempted to set fire to the headquarters of the Basij volunteer militia, which is associated with the Revolutionary Guards, according to news agency reports. At least one man was killed, and several others were injured in that confrontation.
The silent march was a deliberate and striking contrast to the chaos of the past few days, when riot police officers sprayed tear gas and wielded clubs to disperse scattered bands of angry and frightened young people. When the occasional shout or chant went up, the crowd quickly hushed it, and some held up signs with the word silence.
"These people are not seeking a revolution," said Ali Reza, a young actor in a brown T-shirt who stood for a moment watching on the rally's sidelines. "We don't want this regime to fall. We want our votes to be counted, because we want reforms, we want kindness, we want friendship with the world."
In his first public comment on the situation in Iran, President Barack Obama said he was deeply troubled by post-election violence and called on Iranian leaders to respect the democratic process. He told reporters he would continue pursuing a direct dialogue with Tehran, but he urged that any Iranian investigation of election irregularities be conducted without bloodshed.
The key question in Iran's disputed presidential election: How do you count almost 40 million handwritten paper ballots in a matter of hours and declare a winner?
International polling experts and Iran analysts said the speed of the vote count, coupled with a lack of detailed election data normally released by officials, was fueling suspicion around Ahmadinejad's landslide victory.
Mir Hossein Mousavi, Ahmadinejad's reformist challenger, said another rally was planned for today in north Tehran, the hub of his youth-driven campaign and now a nerve center for his opposition movement.
Iran's supreme leader, Ayatollah Ali Khamenei, in a stunning turnaround Monday, ordered an investigation into the allegations of fraud. On Saturday, he had endorsed Ahmadinejad's re-election, calling it a "divine assessment" and appearing to close the door on challenges.
Mousavi says he was robbed of the presidency and has called for the results to be canceled.
Mousavi's newspaper, Kalemeh Sabz, or the Green Word, reported on its Web site that more than 10 million votes were missing national identification numbers similar to U.S. Social Security numbers, which make the votes "untraceable."
Mousavi said some polling stations closed early with voters still in line, and he charged that representatives of his campaign were expelled from polling centers even though each candidate was allowed one observer at each location. He has not provided evidence to support the accusations.
The final outcome was 62.6 percent of the vote for Ahmadinejad and 33.75 for Mousavi — a landslide victory in a race that was perceived to be much closer. Such a huge margin also went against the expectation that a high turnout — a record 85 percent of Iran's 46.2 million eligible voters — would boost Mousavi.
Ahmadinejad, who has significant support among the poor and in the countryside, says the vote was "real and free" and insists the results were legitimate.
"Personally, I think that it is entirely possible that Ahmadinejad received more than 50 percent of the vote," said Konstantin Kosten, an expert on Iran with the Berlin-based German Council of Foreign Relations.
Still, he said, "there must be an examination of the allegations of irregularities, as the German government has called for."
Earlier Monday, Iran's Interior Ministry warned that the mass rally was illegal and would be dealt with severely.
As thousands of Iranians streamed down wide boulevards on foot and motorbikes, however, riot police in helmets and shields stood immobile on the square's rim.
The masses of protesters flashed victory signs and honked car horns. Women wore signs that read, "Where is my vote?"
As Ahmadinejad's embattled government appeared to be trying to limit Internet access and communications in Iran, new kinds of social media were challenging those traditional levers of state media control and allowing Iranians to find novel ways around the restrictions.
Iranians are blogging, posting to Facebook and, most visibly, coordinating their protests on Twitter, the messaging service. Their activity has increased, not decreased, since the election.
On Twitter, reports and links to photos from the mass march through Tehran on Monday, along with accounts of street fighting and casualties around the country, have become the most popular topic on the service worldwide, according to Twitter's published statistics.
Meanwhile, Mousavi's fan group on Facebook has swelled to more than 50,000 members.