TEHRAN, Iran - -Huge swaths of the Iranian capital erupted in fiery riots that stretched into the early hours Sunday as hard-line President Mahmoud Ahmadinejad declared victory in his quest for a second term amid allegations of widespread fraud and reports that his main challenger had been placed under house arrest.
At the same moment the president was promising a "bright and glorious future" for Iran in a late-night televised address, supporters of reformist rival Mir Hossein Mousavi were battling with police and militiamen in riot gear throughout Tehran in the most serious clashes in the capital since a student uprising 10 years ago.
In the streets and squares where young Iranians had danced and waved green banners in support of Mousavi days ago, baton-wielding police chased and beat mobs of hundreds of demonstrators who chanted, "Down with dictatorship!" and "Give me my vote back!" Searing smoke and the smell of burning trash bins and tear gas filled the night sky as protesters ripped up Iranian flags, which had become the symbol of the Ahmadinejad campaign.
Video footage showing unrest in Shiraz emerged early today, but reports of other outbreaks could not be confirmed as authorities tried to limit the scale of the demonstrations by cracking down on electronic communications. Web sites such as Facebook and YouTube were suddenly filtered. For hours Saturday, the Tehran cell phone network was shut down.
Official results released by the Interior Ministry, which is under the control of the president, showed Ahmadinejad with more than 63 percent of the vote - a surprise performance given turnout figures of 80 percent and hours-long lines of city dwellers mostly opposed to Ahmadinejad. Mousavi received 35 percent of the vote, according to the results.
The Obama administration, which has sought to reach out to the Islamic Republic, expressed concern about the results, as many in Iran predicted a new wave of repression to crush the outpouring of civic participation that had swelled during the election season.
"Like the rest of the world, we were impressed by the vigorous debate and enthusiasm that this election generated, particularly among young Iranians," White House spokesman Robert Gibbs said in a statement Saturday. "We continue to monitor the entire situation closely, including reports of irregularities."
Mousavi and fellow reformist candidate Mehdi Karroubi strongly disputed the results in public statements. Karroubi, a former speaker of parliament, called the results "engineered" and "ridiculous."
After security forces prevented journalists from attending an early afternoon news conference he tried to hold, Mousavi, a former prime minister, released a statement alleging a conspiracy to manipulate the vote results, which he claimed showed he was the winner.
"I will not submit to this dangerous charade," he said. He had announced a list of alleged irregularities, including thousands of his poll monitors being barred from voting stations, the previous night. Iran allows no independent observers to monitor the vote.
As the day drew to a close, both campaigns reported that the candidates were under house arrest hours after their offices and affiliated Web sites had been shuttered.
Ayatollah Ali Khamenei, Iran's top political and religious leader, ignored the dispute over Friday's vote and hailed the 80 percent turnout as a great victory for the nation against the plots of its enemies.
"Your epic [victory] was a striking and unprecedented event, in which the political growth, determined political visage and the civic capability and potential of the Iranian nation were beautifully and splendidly displayed before the eyes of the world," he said in a speech broadcast on state television.
The supreme leader's approval means Mousavi supporters have no legal recourse to contest the vote.
But even as the results were released, demonstrators allied with Mousavi defied Iran's restrictions on unauthorized public gatherings and began setting fire to garbage and assembling in rowdy protests.
A demonstration formed in Tehran's Vanak Square in midafternoon. Mostly young protesters, some wearing surgical masks to guard against tear-gas attacks, set fires and blocked traffic as older Iranians stood along the sidelines cheering them on, occasionally joining in the chanting.
Passing drivers honked in support. A woman with her headscarf ripped off screamed defiantly at the stunned security officers who had just beaten her.
Riot police chased demonstrators and some passers-by down streets, beating and bloodying those who refused to move, and running off as the demonstrators fought back with rocks.
Along Mirdadmad Street, a major thoroughfare, shopkeepers urged panicked pedestrians and protesters into their stores for protection, in one instance locking the gate as a group of truncheon-wielding riot police approached. Residents in nearby high-rise towers cheered on the protesters.