A powerful cleric-politician, Akbar Hashemi Rafsanjani, criticised Iran's leadership today on one of the country's most resonant political stages, the Islamic prayer sermon. In a boost for the opposition, he said the leadership must clear up doubts over the disputed presidential election and warned of a "crisis."

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Tens of thousands of opposition supporters packed the weekly prayers at Tehran University, chanting slogans in a show of strength to hear Rafsanjani, who was delivering the sermon for the first time since Iran's election turmoil began a month ago. In the front row was opposition leader Mir Hossein Mousavi, who claims to have won the June 12 election.

Outside the university, more opposition supporters gathered in a rally after the prayers, chanting "death to the dictator" and "coup government, resignation, resignation." Pro-government Basiji militiamen fired volleys of tear gas at the crowd, said witnesses, who spoke on condition of anonymity for fear of government retaliation.

In his sermon broadcast live on radio nationwide, Rafsanjani reprimanded the clerical leadership for not listening to the controversy over the election, which was declared a victory for President Mahmoud Ahmadinejad in results that Mousavi's supporters say were fraudulent.

"Doubt has been created (about the election results)," Rafsanjani said. "There is a large portion of the wise people who say they have doubts. We need to take action to remove this doubt."

Rafsanjani couched his sermon in calls for unity in support of Iran's Islamic Republic. But his sermon was an unmistakable — if implicit — challenge to Supreme Leader Ayatollah Ali Khamenei, who has declared Ahmadinejad's victory valid and demanded an end to questioning of the results.

Rafsanjani said the people's voice must be considered. "We believe in the Islamic Republic ... they have to stand together," he said. "If 'Islamic' doesn't exist, we will go astray. And if 'republic' is not there, (our goals) won't be achieved. Where people are not present or their vote is not considered, that government is not Islamic."

He criticized the postelection crackdown and urged the release of those arrested and said the government reaction had split the nation's clerics. "I hope this Friday prayer sermon will be the beginning of a development and will help us pass safely through this problem, which can be unfortunately called a crisis," he said.

Rafsanjani, a former president, is considered the opposition's top supporter within Iran's clerical leadership. He heads two of the three most powerful clerical bodies that oversee the elected government, the Expediency Council and the Experts Council. He is a bitter rival of President Mahmoud Ahmadinejad and is believed to support Mousavi behind the scenes — his daughter and four other relatives who openly backed Mousavi were briefly detained during protests last month.

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But until Friday's sermon he had avoided commented prominently on the election turmoil. In the days before his widely anticipated sermon, hard-liners have been pressuring him to make clear his backing of Khamenei.

The opposition is hoping their show of strength at the Friday prayers will demonstrate that the movement remains powerful despite suppression by security forces the past month.

After the election, hundreds of thousands marched in the streets in support of Mousavi. But after Khamenei validated the results, police, elite Republican Guards and Basiji militiamen launched a fierce crackdown on protesters in which hundreds were arrested and at least 20 killed — though human rights groups say the figure could be several times that official toll.

The scene outside the university on Friday was tumultuous, as hundreds of Mousavi backers converged on the gates. Before the sermon, police fired tear gas at some trying to enter the prayer. When Mahdi Karroubi, another pro-reform candidate in the June election, headed for the prayers, plainclothes hard-line supporters attacked him, shoving him and knocking his turban to the ground, witnesses said. "Death to the opponent of Velayat-e-Faqih," the hard-liners chanted as they attacked him, referring to the supreme leader, the witnesses said.

As she headed for the university, a prominent women's rights activist, Shadi Sadr, was beaten by militiamen, pushed into a car and driven away to an unknown location, taken away, Mousavi's Web site www.mowjcamp.com and a women's rights site www.meydaan.com said.

After the sermon, hundreds of opposition supporters were outside the gates, chanting slogans against Ahmadinejad.

Inside the prayers — held on a former soccer field covered with a roof — tens of thousands crowded to hear Rafsanjani. Most were Mousavi backers, wearing green headbands or wristbands or had green prayer rugs — the opposition movement's color. They shouted competing slogans with a number of government supporters among the worshippers. Hard-liners made traditional chants of "death to America," while opposition supporters countered with "death to Russia" — a reference to government's ties to Moscow.

In his sermon, Rafsanjani urged unity and appeared to blame hard-liners for disrupting unity by not listening to the controversy over the election. He also spoke openly of the split among Iran's clerics.

Conservative clerics have rallied behind Khamenei, telling their flocks the supreme leader must be obeyed. But many other prominent clerics have been sharply critical or have failed to announce their backing for Ahmadinejad, including most of the country's "maraje'-e-taghlid," or "sources of emulation," Shiite clerics of the highest rank whose religious rulings are closely obeyed by their many followers.

"The maraje'-e-taghlid have always supported and served (the people). Why some of them are offended?" Rafsanjani said. "We need to keep them beside us. We need to support them and rely on them."

Rafsanjani criticized the crackdown on postelection protests, calling for the release of those arrested.

"Sympathy must be offered to those who suffered from the events that occurred and reconcile them with the ruling system. This is achievable. We need to placate them," he told the worshippers in the Tehran University prayer hall.

"It's not necessary ... to keep individuals in jail. Let them join their families. We should not let enemies criticize or laugh at us ... for keeping our people in jail," he said.