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

Iran’s state radio said today that seven people died in clashes in Tehran after an “unauthorized gathering” following a mass rally over alleged election fraud.

The radio report says the seven died in shooting that erupted after several people at the gathering Monday night in western Tehran “tried to attack a military location.”

The report today gave no details. It was the first official confirmation of the shooting in Tehran’s Azadi Square. Witnesses there saw at least one person shot dead and several others seriously wounded after shooting from a compound for volunteer militia linked to Iran’s powerful Revolutionary Guard.

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 — and smaller protests around the country — reinforced what has become increasingly clear 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.

In his first public comment on the Iranian election, President Barack Obama said he was “deeply troubled by the violence I’ve been seeing on TV.”

Although he said he had no way of knowing whether the election was valid, Obama praised protesters and Iranian youth who questioned the results.

Police and other security forces stood by quietly — some sitting on stoops with their batons 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.

Mousavi made his first public appearance since the polls closed, and he launched his claims that the vote was rigged to re-elect the hard-line president.

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

“Respect the people’s vote!” Mousavi cried through a hand-held loudspeaker in Azadi, or Freedom, Square — where Iran’s leaders hold military and political gatherings.

It appeared that Iran’s ruling clerics had opened the door for the demonstration — even giving it news coverage — in a possible bid to avoid more street clashes and seek some breathing room.

But a single moment could change all that. Gunfire erupted from a compound used by the Basij, a volunteer militia linked to Iran’s powerful Revolutionary Guard. An Associated Press photographer saw at least one demonstrator killed and several others with what appeared to be serious wounds.