Security forces and militiamen clashed with thousands of protesters shouting "death to the dictator" outside Teheran University on Monday, beating them with batons and firing tear gas on a day of nationwide student demonstrations, witnesses said. The protests were the largest in months, bringing tens of thousands out in marches at more than a dozen campuses around the country and in several squares in Teheran, as university students - a bedrock of support for the pro-reform movement - sought to energize the opposition. The opposition has been reeling under a fierce crackdown since turmoil erupted over the disputed presidential election in June. Thousands of riot police, Revolutionary Guard forces and pro-government Basij militiamen flooded the area around Teheran University since the morning, vowing to prevent any unrest from spilling out into the streets. They sought to seal off the campus from the outside world. Banners and signs bearing slogans from Supreme Leader Ayatollah Ali Khamenei blanketed the tall university fence, hiding whatever took place inside. Cell phone networks around the universities were shut down, and police and members of the elite Revolutionary Guard surrounded entrances, checking IDs of anyone entering to bar opposition activists, witnesses said. "There's anxiety that there will be violence and shooting. I shout slogans and demonstrate but try not to provoke any clash with the security," one Teheran University student, Kouhyar Goudarzi, told The Associated Press in Beirut by telephone. "We are worried." The fiercest violence was on the streets outside. Thousands of protesters massed outside Teheran University in support of the students, chanting "death to the dictator," the witnesses said. Riot police fired tear gas and Basij militiamen, some on motorcycles, charged the crowds. The plainclothes Basijis beat protesters on the head and shoulders as the crowd scattered, then regrouped on nearby street corners, setting tires on fire to ward off the stinging tear gas. Nearby, protesters and Basijis pelted each other with stones, the witnesses said, speaking on condition of anonymity for fear of retaliation. Shots were heard fired on nearby Enghelab Street, witnesses said. Pro-opposition Web sites reported that at least one protester was wounded in the area, but the reports could not be independently confirmed. Inside Teheran University, hard-line students loyal to the government clashed with protesters in scuffles and fist-fights. In one photo obtained by The Associated Press, a pro-reform student wearing a green headband had blood streaming down his face after a beating. A young woman, overcome by tear gas, slumped to the ground, as two other students tried to help her. Several thousand students marched through the campus, many of them wearing surgical masks or scarves over their faces to protect against tear gas, according to photos from the scene obtained by AP. Some wore green wristbands and waved green balloons, the color of the opposition movement of Mir Hossein Mousavi. 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. At the same time, the hard-line students - numbering about 2,000 - held their own march through the university, waving pictures of Khamenei and Iranian flags and chanting "death to the hypocrites," a reference to Mousavi and other opposition leaders. Protests erupted at seven other universities in Teheran and on campuses on at least six other cities, the New York-based International Campaign for Human Rights in Iran reported. At Teheran's Amir Kabir University, Basiji militiamen entered the campus and tried to break up a march by students, witnesses said. The Basijis pushed and shoved the students, dragging some away. At Sharif University, Teheran's premier technology university, thousands of students blocked the main road leading into the campus, witnesses said. Police outside the us There was no immediate word on arrests or injuries from the unrest. Journalists working for foreign media organizations, including the AP, were banned from covering Monday's protests. They were told late Saturday by the Culture Ministry that their press cards would be suspended for three days starting Monday. Mousavi threw his support behind the marches, declaring that his movement was still alive and that the clerical establishment was losing legitimacy in the Iranian people's minds. "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 presidential election. Friday's were the biggest protests in months - larger than the last major rallies on Nov. 4. The size was a sign of how the young and particularly university students have become the most fervent proponents of street action. Mousavi and fellow pro-reform politicians have struggled to keep their movement's enthusiasm stoked after the fierce crackdown launched after the disputed elections, which the opposition says President Mahmoud Ahmadinejad won by fraud. In the weeks after the election, hundreds of thousands marched in the street against Ahmadinejad, but the protests were crushed by a wave of arrests against protesters, politicians and activists. Since then, the opposition have only managed to hold smaller protests of several thousands - and only by timing the marches to coincide with significant national events to help drum up a crowd. Monday's protests were held on National Students Day, an annual occasion when student rallies are traditionally held. Khamenei, the supreme leader who has final say on all state matters, accused the opposition Sunday of causing divisions in the country and creating opportunities for Iran's enemies. Authorities have arrested well over 100 student leaders in past weeks, looking to blunt Monday's protests. On Saturday, police detained 15 women from the Committee of Mourning Mothers, which groups relatives of protesters who have been killed in Iran's postelection crackdown. The women were arrested at a Teheran park where they have held weekly protests for months, the International Campaign for Human Rights in Iran. Authorities also slowed Internet connections to a crawl in the capital. For some periods on Sunday, Web access was completely shut down - a tactic that was also used before last month's demonstration. Students at Teheran University played a major role in street demonstrations in support of the 1979 Islamic Revolution that toppled to pro-US shah and brought clerics to power. But in the past decade, universities have become strongholds for the pro-reform opposition, which seeks to reduce the clerics' domination of politics.