Tens of thousands of students, many shouting "Death to the Dictator!" and burning pictures of Iran's supreme leader, took to the streets on more than a dozen campuses Monday in the biggest anti-government protests in months.
Riot police and pro-government Basij militiamen on fleets of motorcycles flooded Tehran's main thoroughfares, beating men and women with clubs as crowds of demonstrators hurled bricks and stones. Some protesters set tires and garbage cans ablaze.
"Death to the oppressor, whether it's the shah or the leader!" the students chanted, according to witnesses _ making a daring comparison between Supreme Leader Ayatollah Ali Khamenei and the pro-U.S. shah, despised in Iran since his overthrow in the 1979 Islamic Revolution.
The protests reflected how university students _ the driving force of the 1979 Islamic Revolution _ have revitalized the anti-government movement even as mainstream opposition politicians struggle to dent the power of President Mahmoud Ahmadinejad and Iran's clerical leadership.
Inside the walled campus of Tehran University, fistfights broke out between protesters and hard-line students loyal to the government. In one photo obtained by The Associated Press, a student wearing a green headband _ the opposition's signature color _ had blood streaming down his face after a beating. In another, a young woman, overcome by tear gas, slumped to the ground, as two other students tried to help her.
Journalists working for foreign media organizations, including the AP, have been banned from covering opposition protests, including Monday's demonstrations.
A fierce government crackdown crushed gigantic protests by hundreds of thousands that erupted immediately after June's disputed presidential elections, which the opposition says Ahmadinejad won by fraud. The wave of arrests swept up not only protesters but also many pro-reform politicians and activists, deeply damaging the movement.
Since the summer, the opposition has been able to hold only about one protest a month, all far smaller than the ones in June and July.
Monday's mass mobilization was unlikely to mean a new wave of more frequent protests _ activists say escalation remains difficult under the crackdown. But the large turnout showed that even months of intense arrests and intimidation have failed to stamp out the movement.
Opposition leader Mir Hossein Mousavi declared the clerical establishment was losing legitimacy in the eyes of Iranians.
"A great nation would not stay silent when some confiscate its vote," said Mousavi, who claims to be the real winner of the June 12 election.
Thousands of riot police, Revolutionary Guard forces and Basij militiamen surrounded Tehran University beginning at dawn, vowing to prevent any unrest from spilling out into the streets.
They sought to seal off the campus from the outside world, draping the university fence with banners and signs bearing slogans from Khamenei to hide what took place inside.
Cell phone networks were shut down, and police and members of the elite Revolutionary Guard surrounded entrances, checking IDs to prevent opposition activists from entering, said witnesses. They, like all those who spoke to the AP, requested anonymity for fear of retaliation.
Authorities also slowed Internet connections to a crawl in the capital to stifle activists' communications.
Still, large crowds massed in the streets outside the university in support of the students, chanting "death to the dictator!" and taunting the plainclothes Basij militiamen.
Footage posted on YouTube showed some protesters burning pictures of Khamenei _ breaking a major taboo against insulting the supreme leader, who stands at the pinnacle of Iran's clerical leadership.
As riot police fired tear gas, militiamen charged the crowds, beating people on the head and back, witnesses said. The youths regrouped on street corners, where they set tires and garbage on fire and pelted the militiamen with stones and bricks, according to witnesses and footage posted by the opposition on the Internet.
Witnesses said many protesters were arrested on Monday, while the semiofficial Fars news agency cited a judiciary statement saying an unspecified number of arrests took place and those in custody were being interrogated.
In Washington, State Department spokesman Ian C. Kelly condemned the "continued harassment, arbitrary detention, and conviction of individuals for their participation in peaceful demonstrations."
Inside Tehran University, several thousand pro-reform students marched through the campus, many wearing surgical masks or scarves over their faces to protect against tear gas, according to photos from the scene obtained by the AP. Some wore green wristbands and waved green balloons.
Hard-line students _ numbering about 2,000 _ held a counter-demonstration in the university, waving pictures of Khamenei and Iranian flags and chanting "death to the hypocrites," a reference to Mousavi and other opposition leaders, official media reported.
Protests spread to nearby streets and squares. Gun shots were heard on nearby Enghelab Street, witnesses said, and pro-opposition Web sites reported that at least one protester was wounded in the area. Another Web site, Fararu, reported that a female student was thrown from a second-story window during a protest in the western city of Hamadan. Neither report could be independently confirmed.
Protests erupted at seven other universities in Tehran and on campuses in at least six other cities, the New York-based International Campaign for Human Rights in Iran reported.
Thousands demonstrated at Tehran's Polytechnic University chanting, "You traitor Mahmoud (Ahmadinejad) ... You destroyed our homeland." At Tehran's Amir Kabir University, Basiji militiamen tried to break up a march, pushing and shoving students and dragging some away.
Students played a major role in demonstrations in support of the 1979 revolution that toppled the shah and brought the clerical leadership to power. But in the past decade, universities have become strongholds for the pro-reform opposition, which seeks to reduce the clerics' domination.
Monday's protests were the largest in months _ far bigger than the last major rallies on Nov. 4. The opposition has begun timing its marches to coincide with significant national events to help drum up a crowd. Monday's protests were held on National Students Day, when student rallies are traditionally held.
The most senior opposition supporter in the clerical leadership made a rare public show of backing for the students in comments over the weekend. Akbar Hashemi Rafsanjani, a former president who usually works behind the scenes, warned that "suppression is not the way to run a country."
"Most students are protesting the existing situation," he said. "My heart breaks when I see that students are suppressed."
AP correspondents Scheherezade Faramarzi in Beirut and Lee Keath in Cairo contributed to this report.