Gunshots were fired during a rally for Iranian opposition leader Mir Hossein Mousavi in Tehran Monday, after hundreds of thousands of supporters gathered to protest the disputed presidential elections, according to witnesses and news accounts.
At least one person is reportedly dead. Witnesses told the AP and Reuters that an unknown number of protesters were shot by pro-government militia, after a handful of demonstrators entered the militia compound near the site of the rally in Tehran's Freedom Square.
"The shots came from the roof," an eyewitness said. "They hit a car with protesters riding on top. One man was hit and flung from the car. It was awful."
An Associated Press photographer told ABC News he saw pro-government militia fire at opposition protestors, killing one.
But a Mousavi supporter who was at the rally told ABC News she saw a male protester shot and injured in the leg or foot, and taken to a hospital.
Mousavi appeared at the rally before shots were fired at the crowd, and spoke briefly to his supporters, urging calm. It was the defeated candidate's first appearance since election day.
"I'm ready to pay any price to realize your ideals," he said to his supporters. "We have to stand up to this astonishing charade."
Iran's state television also reported that shots were fired during the rally and that people were seen running away.
The large rally was held despite the Iranian interior ministry refusing a request by Mousavi for permission to hold a rally. Unlike previous protests dominated by young people, today's mixed young and old, students and professionals.
Throngs of protestors shouting "Mousavi" showed up to the protest Monday, despite fears of a violent crackdown.
"It's very clear, clear as daylight, you see the crowd. The government has really changed the results," said one Mousavi supporter at the rally.
Others chanted demands of another revolution.
Mousavi addressed the crowd from the roof of his car.
"The vote of the people is more important than Mousavi or any other person," Mousavi said, according to the BBC.
Earlier today, Iranian TV announced that Iran's supreme leader Ayatollah Khamenei ordered an investigation into claims of fraud in the contested presidential elections held last Friday.
The announcement came hours after the government banned a rally by supporters of Mousavi in Tehran and other Iranian cities.
Khamenei has asked the exclusive Guardian Council to examine charges by Mousavi of widespread vote rigging during the election, but there is uncertainty whether that will have any substantial impact.
"There is that concern that perhaps this is just a tactical shift and it won't lead to anything because there may be some wrongdoing in that process as well," said Trita Parsi, founder and president of the National Iranian American Council.
The United States and other countries denounced the violence.
"It is up to Iranians to make decisions about who Iran's leaders will be. We respect Iranian sovereignty," President Obama said Monday.
The president said he would continue to pursue a "tough direct dialogue" between the U.S. and Iran. Yet, he said he was deeply troubled by the violence he saw on television in Iran.