TEHRAN, Iran  — Hundreds of protesters called for the death of Iran's (search) supreme leader Ali Khamenei (search) as thousands of onlookers watched early Friday, the third day of demonstrations in the capital despite threats by the hard-line regime to crack down to end the disturbances.

The three nights of demonstrations have produced the largest outpouring of public opposition against Iran's leadership in months, involving hundreds of young Iranians, some still teenagers.

They shouted chants including, "Khamenei the traitor must be hanged," "Guns and tanks and fireworks, the mullahs must be killed," and "student prisoners must be freed," witnesses said.

The demonstrators concentrated in two areas, around Tehran University (search) and near the Intercontinental Hotel, though the protesters had left the university area late Thursday night.

Before they dispersed, police had prevented some two dozen pro-Khamenei vigilantes on motorcycles -- at times chanting "oh the exalted leader, we are ready to follow your instructions," -- from confronting the students.

Thousands of people looked on, sometimes clapping with the protesters and taking up their chants. Residents near the university hospital left their doors open so that demonstrators could find quick shelter if the authorities cracked down.

Similar scenes were evident near the hotel, where about 500 hard-liners on motorcycles chased down protesters, beating them with cattle prods and circling around, gunning their engines, witnesses said. Some onlookers struck back at the vigilantes, hitting them with their fists. Near the hotel, two motorcycles were set aflame.

Riot police later rushed the crowd near the hotel, dispersing the demonstrators and sending the onlookers running. Even as it approached 2 a.m. Friday, traffic was bumper-to-bumper in downtown Tehran as curious residents stayed out to watch developments.

Though the demonstrators seemed disorganized, with no apparent leadership, the country's hard-line clerics were clearly taking them seriously.

Khamenei, in a speech broadcast on state television and radio, referred to violence in 1999 when security forces and extremist supporters of hard-line clerics attacked students protesting media restrictions. At least one student was killed and the clash touched off the worst street battles since the 1979 revolution that ousted the U.S.-backed shah.

"If the Iranian nation decides to deal with the (current) rioters, it will do so in the way it dealt with it on July 14, 1999," Khamenei said.

"It should not be allowed that a group of people contaminate society and universities with riots and insecurity, and then attribute it to the pious youth," he said.

But the protesters ignored Khamenei's warning. Some in the crowd urged demonstrators to gather again after a soccer match Friday night between two popular teams. They said demonstrations would continue until the July anniversary of the 1999 protests.

Reformist newspapers, which reflect the thinking of some established politicians who have been fighting for change for years, offered little commentary on the unrest the two days before.

The young demonstrators face a determined foe that has defied popular calls for reform for years and is likely to justify anything done to restore calm -- including violence -- in the name of Islam.

Exiled opposition groups, on the other hand, have seized the opportunity created by restless Iranian youth, encouraging dissent through avenues like Los Angeles-based Persian TV channels. U.S. pressure on Iran, which Washington accuses of hiding a nuclear weapons program and harboring terrorists, may have further emboldened those who hope to see the regime toppled.

Late Thursday, hundreds of police locked down central Tehran and blocked off all streets leading to a dormitory housing Tehran University students. Police also prevented people from gathering in the streets.

About 200 students milled inside the dormitory grounds, occasionally throwing stones from behind the main gate at the police, who did not respond, according to an Associated Press reporter at the scene.

People on foot and carloads of interested onlookers converged on the scene to take in the overwhelming police presence and apparently to witness any repeat of the previous two nights' clashes, but were prevented from going anywhere near the dormitory.

Demonstrators also called for the resignation of President Mohammad Khatami, a popularly elected reformist, accusing him of not pushing hard enough for change.

Khatami doesn't have the power of unelected hard-liners who control the judiciary and the security forces. But the hard-liners don't have popular support, leaving Iran at a stalemate.