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.
"Even as we do so it would be wrong for me to be silent about what we've seen on the television over the last few days," he said. "What I would say to those people who put so much hope and energy and optimism into the political process, I would say to them that the world is watching and inspired by their participation regardless of what the ultimate outcome of the election was." A State Department spokesman said that the United States is "deeply troubled by the reports of violence, arrests and possible voting irregularities."
"The essential right of people, to express themselves peacefully, needs to be respected. The international community remains committed to seeing Iran living up to its international responsibilities, and we will continue to use all avenues to try to convince Iran to meet its international obligations," said spokesman Ian Kelly. "Iran needs to take these allegations of misconduct or of election irregularities seriously."
"I think there are a number of factors that give us some concern about what we've seen," Gibbs said.
This weekend, Vice President Biden said that the United States was waiting and watching the events in Iran, but that the election was not "as clear cut as they make it sound."
UN Secretary General Ban Ki-Moon was also careful about commenting on election results..
"The position of me and the United Nations is that the genuine will of the Iranian people should be fully respected. I am closely following how this investigation into this election result will come out," Ki-Moon said Monday. "As of now, I have to watch all this situation, how it evolves."
President Mahmoud Ahmadinejad was declared the winner over the weekend by what was called "a large margin."
Ahmadinejad also hinted that his challenger may face punishment for continuing his fight against disputed election results, but his followers are not backing down.
Some experts are unsurprised by the claims of voter fraud. "In my view, this has never been a democracy," author and New York Times contributor Thomas Friedman said on "Good Morning America." "The whole thing is a fraud. The only reason they hold elections there is to reinforce the autocracy of the mullahs."
But what this election does reflect is the rise of moderate voices.
"I think what we are seeing is basically an upsurge of the moderates across the region," he told "GMA's" Robin Roberts. "What's new, what we're seeing is, historically, in the Middle East, the extremists went all the way and the moderates just tended to go away. And what you're seeing here is now the moderates not being willing to go away but we all always have to remember the forces of extremism there are extremely well armed, they are extremely ruthless and they are not going to give up."
According to Friedman, Ahmadinejad's government will likely put up a fight against any challenges.
"This regime in Iran will do whatever it takes to stay in power," he said.
This morning, word came of a police raid on Tehran University, where cops are said to have destroyed computers and ransacked dorm rooms. Dozens of students are also said to have been arrested.
According to the AP, some 3,000 students held a nighttime gathering Sunday, chanting, "Death to the dictator." The crowd then began to throw rocks and Molotov cocktails at assembled police officers who fired back with plastic bullets and tear gas, according to a student eyewitness who spoke to the AP.
The student, who would only give his first name, Akbar, out of fears for his safety, told the AP that the crowd threw stones and bricks at the police and set a truck and other vehicles on fire. Hardline, pro-Ahmadinejad volunteers retaliated by ransacking dorm rooms, smashing furniture and computers with axes and sticks, before policemen grabbed memory cards and computer software. Police left at around 4 a.m., according to Akbar.
"Many students are now leaving to go home to their families, they are scared," he told the AP. "But others are staying. The police and militia say they will be back and arrest any students they see."
"I want to stay because they beat us and we won't retreat," he added.
Tehran University was the site of serious clashes against student-led protests in 1999 and is one of the nerve centers of the pro-reform movement in Iran. Today's rally by Mousavi supporters was meant to commence there.
Young Iranians Clash With Police; Cops Fight Back With Tear Gas
It was a weekend full of turmoil here, the protests sparked when the government declared hard-liner Ahmadinejad the landslide winner over his more moderate challenger, Mirhossein Mousavi, who many here believed had been leading the race.
Through the night, young Iranians set the streets on fire, venting their anger at an election they insist was stolen by the incumbent president.
The violence continued today as demonstrators were attacked by police with tear gas and batons. We saw young women sprayed in the face with pepper spray, and armor-clad police attacking protesters from the backs of speeding motorcycles. The police revoked our permission to film, so we recorded the protests on our cell-phones.
Crowds of protestors lashed back with sticks, rocks and seemingly anything they could get their hands on. Protestors forced police officers off a motorcycle and burned it. Demonstrators expressed their anger, with one saying, "This election will not stand. ? We are angry. ? We have been cheated." Over the weekend, crowds gathered, chanting, "Down, down with the dictator," referring to the president.
Near the opposition protests Sunday, President Ahmadinejad made a show of his own popular support. Tens of thousands of people filled a central Tehran square, expressing their fervent support of the sitting president. There were no police present at this gathering.
At the pro-government demo Sunday, a young female chador-clad supporter of the president told us "these people, millions of them, they like the president." She added that she had cast her vote in favor of Ahmadinejad.
At a press conference, the president dismissed the opposition protestors, comparing them to excited crowds after a soccer match.
Mousavi is now left with dwindling options. Two presidential candidates, Mousavi and Karroubi, have now officially challenged the election results. Mousavi has asked clerics to declare a fatwa and asked the country's powerful religious leaders to reverse the results.
Iran's Guardian Council to Rule on Vote in 10 Days
According to the AP, Mousavi also asked Iran's top legislative body, the Guardian Council, to annul the result. The Guardian Council, whose chairman, Ayatollah Ahmad Jannati, endorsed the president prior to the vote, has said that it will rule on the matter within 10 days.
Meanwhile, Iran's supreme religious leader, Ayatollah Ali Khamenei, the most powerful man in the country, declared the election fair and ordered Iranians to respect the result.
But, according to the AP, Iranian state television reported that Ayatollah Khamenei has ordered an investigation into the claims of election fraud. The contradictory reports make it difficult to verify what is and isn't misinformation.
Across the country, the government continued to block text-messaging as well as access to YouTube and Facebook, which opposition supporters had used to organize demonstrations.
What they didn't block was Twitter, which protesters then took advantage of to attack the government and share information about the crackdown.
In Iran itself, the situation continues to be volatile. Today, in Moscow, the Iranian Embassy said Ahmadinejad has put off a visit to Russia and said it was unclear whether the president would travel at all. Ahmadinejad had been expected to visit the Russian city of Yekaterinburg and meet with Russian President Dmitry Medvedev on the sidelines of a regional summit.
ABC's Jake Tapper, Lara Setrakian and The Associated Press contributed to the reporting of this story.