Demonstrators called Mr. Ahmadinejad a liar, offered roses to police officers or walked in silence with green tape over their mouths. At other times, they shouted, “We are Mousavi’s Green Army.”
Several held aloft signs in Persian and English asking, “Where is my vote?” in a reference to the lower-than-expected vote attributed to Mr. Mousavi and reformist cleric Mehdi Karroubi, who also appeared at the rally. Both men and the third opponent to Mr. Ahmadinejad — Mohsen Rezaie, a former commander of the Revolutionary Guards — have demanded an investigation of the vote tally, which gave Mr. Ahmadinejad 63 percent of votes cast.
Other demonstrators called Mr. Ahmadinejad’s purported victory a coup d’etat and demanded that his government resign.
Some revived slogans from the Islamic revolution such as Marg bar Zolm (Death to Injustice), which another generation’s protesters had chanted at anti-Shah rallies.
“Why should a person who got 24 million votes have to defend his vote with clubbing and riot police?” asked Mansour Gholamali, 46, an office worker. “From the day after the election, all the streets were as if they were under the control of a military government who came to power through a coup d’etat.”
“I was around in 1979,” said Golzamaneh Rezai, 55, a retiree who struggles to make do on a monthly salary equivalent to about $300. “We had our revolution in order to achieve freedom and once again we’re now demanding the same thing: freedom and a share in the oil receipts.”
One protester was fatally shot by members of the Basij, a paramilitary group, during a face-off outside a military base close to Freedom Square. Five students were killed Sunday night when their dormitory at Tehran University was attacked. More than 100 students were arrested.
Mr. Obama said Monday that he was “deeply troubled” by the election fraud allegations and “it would be wrong for me to be silent” about the violence and suppression of free speech, but that the United States would continue to pursue “tough, hard-headed diplomacy” with a country that many think is close to developing the capability to make nuclear weapons and has growing influence in the Middle East.
J. Scott Carpenter, a former deputy assistant secretary of state who oversaw the George W. Bush’s administration’s Iran democracy program, said, “The Obama administration should take advantage of regime weakness to increase its pressure on Tehran both rhetorically, by siding strongly with the Iranian people, and reconsider its decision to mothball the Iran democracy program.”
However, former President George H.W. Bush, while expressing skepticism about the official election results, said the U.S. should be prudent in reacting to events in Iran.
“They ought to get to the bottom of it,” he said on the debut broadcast of The Washington Times’ “America’s Morning News.” “And without emotion go forward and see if there is something that can be done from outside without inflaming tensions; we don’t want to inflame tensions with Iran.”
He added that Mr. Obama should refrain from making any military threats.
As cries of “Allahu Akbar” (God is Great) marked the dispersal of the Tehran rally, thick plumes of smoke rose into the darkening sky. Bystanders variously ascribed the smoke to rioting outside a Basij base, the burning of paramilitaries’ motorcycles, or the torching of a gas station.
“Since the revolution, we’ve never seen anything like this,” said Hossein, an engineer who gave only his first name. “These people are here to defend their republic.”
In keeping with the religious tone of the event, not a single woman removed her head scarf and rules of Islamic morality were maintained throughout.