TEHRAN, Iran - In a massive outpouring reminiscent of the Islamic Revolution three decades ago, hundreds of thousands of Iranians streamed through the capital yesterday, and the fist-waving protesters denounced President Mahmoud Ahmadinejad's claim to victory in a disputed election.

Standing on rooftops, pro-government gunmen opened fire on a group of protesters who had tried to storm the militia's compound. One man was killed and several others were wounded in the worst violence since the disputed election Friday.

Angry men showed their bloody palms after cradling the dead and wounded who had been part of a crowd that stretched more than five miles supporting reform leader Mir Hossein Mousavi.

The huge rally reinforced what has become increasingly clearer since the election: The opposition forces rallying behind Mousavi show no signs of backing down. Their resolve appears to have pushed Iran's Islamic establishment into attempts to cool the tensions after days of unrest.

Police and other security forces stood by quietly - some sitting on stoops with their clubs and shields resting behind them as the marchers swallowed the streets in parts of Tehran. Estimates put the turnout at hundreds of thousands overflowing the square, where crowds of 200,000 have filled the plaza in the past.

Brief clips of the march were shown on state television in an extremely rare nod to anti-government attacks.

International polling experts and Iran analysts said the speed of the vote count - of 40 million handwritten ballots - coupled with a lack of detailed election data normally released by officials, was fueling suspicion about Ahmadinejad's landslide victory.

Iran's supreme leader endorsed the hard-line president's re-election the morning after Friday's vote, calling it a "divine assessment" and appearing to close the door on challenges from Iran's reformist camp. But in a stunning turnaround yesterday, after two days of rioting in the streets, he ordered an investigation into the allegations of fraud.

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." It did not say how it knew that was the case. *