http://www.nytimes.com/2009/06/20/world/middleeast/20iran.html?_r=1

TEHRAN – Iran ’s supreme leader, Ayatollah Ali Khamenei, sternly cut off any compromise over the nation’s disputed elections on Friday. In a long and hard-line sermon, he declared the elections valid and warned of violence if demonstrators continue, as they have pledged, to flood the streets in defiance of the government.

Opposition leaders who failed to halt the protests, he said, “would be responsible for bloodshed and chaos.” The tough words seemed to dash hopes for a peaceful solution to what defeated candidates and protesters call a fraudulent election last week, plunging Iran into its gravest crisis since the Islamic Revolution in 1979.

“Flexing muscles on the streets after the election is not right,” he said, before tens of thousands of angry supporters at Tehran University. “It means challenging the elections and democracy. If they don’t stop, the consequences of the chaos would be their responsibility.”

But opposition leaders, who stayed home Friday, called for yet another huge rally on Saturday afternoon, setting the stage for a possible showdown between protesters and security forces, perhaps a violent one.

The sermon put Ayatollah Khamenei, who prefers to govern quietly and from behind the scenes, at the forefront of a confrontation not only among factions of the government but among Iranians themselves.

It also presents Mir Hussein Moussavi, whom the opposition says was the real winner of last Friday’s elections, with an excruciating choice. The former prime minister and long-time insider must decide whether to escalate his challenge to Iran’s supreme leader and risk a bloody showdown, or abandon his support for a popular uprising that his candidacy inspired.

During the tough sermon, Ayatollah Khamenei tried to tamp down factional disputes among the elite, at one point even chastising pro-government militias and President Mahmoud Ahmadinejad for their role in the crisis. But he hardened his stance on the election results. On Monday, a crowd that the mayor of Tehran estimated at three million rallied for the first of four days, and Ayatollah Khamenei ordered an investigation into the election results, which declared Mr. Ahmadinejad the winner, with 63 percent to Mr. Moussavi’s 34 percent. Then on Wednesday, the government invited Mr. Moussavi and the other two presidential candidates to meet with the Guardian Council, the powerful body that oversees the elections.

But the ayatollah said Friday that there was nothing to discuss, as he again endorsed the victory of Mr. Ahmadinejad, seated in the audience, and called the elections “an epic moment that has become a historic moment.” He dismissed allegations of fraud.

“Perhaps 100,000 votes, or 500,000, but how can anyone tamper with 11 million votes?” he asked as the crowd burst into laughter. “If the political elite ignore the law – whether they want it or not – they would be responsible for the bloodshed and chaos,” he said.

He added that foreign agents were behind the street unrests and that there were efforts to stage a “velvet revolution.”

“They thought Iran is Georgia,” he said, adding, “Their problem is that they don’t know this great nation yet.”

Tens of thousands of Mr. Ahmadinejad’s supporters gathered for the sermon. Television showed the streets filled with people near Tehran University.

Newspapers said Thursday that a group of members of Parliament reported that the paramilitary forces of Basij were responsible for the attack on a dormitory in Tehran and a housing complex called Sobhan this week. Students said that five students – two women and three men – were killed in the attack.

In his sermon, Ayatollah Khamenei criticized those who carried out the attack. “Have you calculated the impact of going to the dormitories in the name of the leader?” he asked. “Muscle-flexing after elections is not right. Put an end to this.”

The nation’s complex politics and maneuvering were on display in the sermon when he defended an influential politician and former president,Ali Akbar Hashemi Rafsanjani , a bitter rival of Ayatollah Khamenei’s who many Iranians say is a major force in challenging the election.

Ayatollah Khamenei criticized Mr. Ahmadinejad for accusing Mr. Rafsanjani, his children and a former speaker of Parliament, Ali Akbar Nateq Nouri, of corruption during a televised debate, saying that both had risked their lives for the revolution.

“No one had accused them of corruption,” he said. But he did not remove the cloud of suspicion from Mr. Rafsanjani’s children, noting that there had been accusations, unproven, against them.

There was no immediate reaction from Mehdi Karroubi, another presidential candidate who accused the government of fraud. Many analysts and aides to Mr. Moussavi have been arrested and were not available for comments. But the human rights group Amnesty International warned that Ayatollah Khamenei’s speech indicated that the authorities were willing to conduct a violent crackdown.

“We are extremely disturbed at statements made by Ayatollah Khamenei which seem to give the green light to security forces to violently handle protesters exercising their right to demonstrate and express their views,” the group said in a statement.

In a letter on Friday, Mr. Karroubi urged the Guardian Council to nullify the elections. “This is not the demand of an individual, it is the demand of the people,” he wrote in a letter posted on his Web site. “I warn you that insulting people would only intensify their rage.”

The council is expected to meet with the three presidential candidates on Saturday.

Web sites associated with both Mr. Moussavi and Mr. Karroubi said that the large rally scheduled for Saturday was still on.

In Paris, a friend of Mr. Moussavi’s who said he was acting as his spokesman said Friday that Ayatollah Khamenei’s statements would be met by large demonstrations.

“What happened is beyond cheating,” the friend, Mohsen Makhmalbaf, a film director, said in a hastily organized news conference in Paris. “Since Friday, a 30-year-old page was turned. We’ve fallen into dictatorship. For the first time in 30 years there have been grass-roots demonstrations with millions of people, and these demonstrations stand as a proof that people want democracy.”

His daughter Samira, also a filmmaker, said, “Until Friday we had 80 percent dictatorship and 20 percent democracy, and since Friday we have 100 percent dictatorship.”