Opposition leader Mir Hossein Musavi at a rally in Tehran

President Mahmud Ahmadinejad delivers the weekly Friday Prayer sermon at Tehran University.

A hundred thousand people rallied to mark Quds Day in Tehran.

Iran Election Special Iran Election Special RFE/RL's Full Coverage Following the disputed reelection of Iranian President Mahmud Ahmadinejad, supporters of Mir Hossein Musavi have taken to the streets to protest. Following the disputed reelection of Iranian President Mahmud Ahmadinejad, supporters of Mir Hossein Musavi have taken to the streets to protest. Click here for news, blogs, and analysis of the presidential election and aftermath.

Tens of thousands of people wearing green accessories -- the sign of the opposition -- have come out on to the streets of Tehran and other major cities for the first mass protests against the Iranian government in two months.Clashes were reported between the opposition protestors and supporters of President Mahmud Ahmadinejad, backed by police and Basij militia vigilantes. It is not yet known how many protesters were arrested.The protesters took advantage of the officially sanctioned observance of Quds (Jerusalem) Day -- on which Ahmadinejad denounced the Holocaust as a "myth"-- to assemble without immediately being spotted and stopped by the police.Shouting slogans, the protestors denounced Ahmadinejad as stealing the June presidential election: "Liar, liar, where is your 63 percent?"They also demanded the release of thousands of people arrested in government crackdowns on previous rallies against Iran's contested presidential election results.Demonstrations also took place in other major Iranian cities including Isfahan, Mashhad, Qom, Shiraz, and Tabriz.One woman protester told RFE/RL's Radio Farda by phone that "thousands of people" are out in green, including Mehdi Karrubi, a former speaker of parliament and opposition leader. She did not give her name for fear of being later identified by the police."People are now heading to Karimkhan Square. I can tell you that from Vali Asr Square to Karimkhan Zand Square all is covered in green," she added. "The conservatives are much fewer than the reformists."Karrubi has led opposition charges that some of those arrested in earlier protests were raped in jail -- charges that have deeply divided the Iranian public over the government's treatment of the opposition movement.But the Iranian state news agency IRNA reported that leading opposition leader Mir Hossein Musavi was forced back by hard-liners when he also tried to appear. The agency said government supporters attacked his car, shouting "death to the hypocrite," until he drove off, unhurt.Musavi, who finished second in the contentious June presidential election, has charged the government with massive vote fraud to secure a second term for Ahmadinejad.A reformist website, parlemennews.ir, said that hard-liners also attacked former reformist President Mohammad Khatami, but that he was rescued by riot police."During the scuffle, his turban fell off and they wanted to beat him but supporters resisted them and the riot police promptly intervened," the website said.Khatami’s brother, Mohammad Reza Khatami, later told AFP that the former president was unhurt.The situation is extremely volatile not only because security forces warned ahead of the events that they would "deal decisively" with any protests, but because masses of Ahmadinejad supporters are also in the streets.There were reports of fistfights breaking out between the opposition supporters and hard-liners as the two camps move through the streets with no clear lines separating them.Some witnesses have also reported security forces clashing with opposition supporters and arresting an undetermined number of people.Ahmadinejad himself was among some 100,000 people who marched towards Tehran University from different parts of the capital for official ceremonies marking Quds Day.As they marched, the chanted: "America, we know what your plan is. America, Israel, this is the last message to you. The army of justice is ready to rise."Ahmadinejad later used a keynote speech at Friday Prayers at the mosque of Tehran University to lambast the Israeli government and repeat his frequent declaration that the Holocaust is a "myth.""The very existence of this [Israeli] regime is an insult to the dignity of the people," he said. "They [Western powers] launched the myth of the Holocaust. They lied, they put on a show, and then they support the Jews."Many of the opposition leaders, including Musavi, and Karrubi, are former office holders and senior members of the ruling Iranian establishment. That makes the continuing dispute over the election results the biggest domestic political crisis the Islamic republic has faced in its 30-year history.In a sign of the split in the ruling establishment over the election, former President Akbar Hashemi-Rafsanjani was replaced with a hard-line cleric to give the sermon during Friday Prayers at Tehran University marking Quds Day.It marked the first time in decades Rafsanjani had been replaced for the annual event. Rafsanjani backed Musavi in the election and has been strongly criticized by hard-liners for speaking out during a Friday Prayer sermon in July against the conduct of the election.Rafsanjani, in an apparent bid to defuse tensions over the snub, told Iranian state television's Arabic-language broadcaster, Al-Alam, that "I don't think it is necessary that I always deliver the sermon this day after 30 years."In his place, the Friday Prayers sermon -- which is heard nationwide -- was delivered by hard-line cleric Ahmad Khatami.The Islamic Revolutionary Guards Corps warned the opposition on September 17 that it would tackle any "divisive and antirevolutionary movement" during the Quds Day observances.The Revolutionary Guards said in a statement, ""We are warning people and the movements who want to help the Zionist regime that if you seek any disruption or disorder during the glorious Quds Day rally, you will be decisively confronted by the courageous children of Iran."The opposition says at least 72 protesters were killed in previous violence that followed the election, while government officials maintain that only 36 died in the unrest.