Tuesday Iran threatened tougher action against protesters . Meanhile, more than 200 were arrested during marches by tens of thousands at universities across the country.
The warning suggested that Monday's unrest raised authorities' concern that the protest movement could pick up new steam. The protests Monday turned into fierce clashes between youths throwing stones and riot police and militiamen wielding batons and tear gas.
Perhaps more importantly, they also saw an increased fervor and boldness among demonstrators, who more openly broke the biggest taboo in Iran -- burning pictures of Supreme Leader Ayatollah Ali Khamenei and chanting slogans against him.
The turnout, fueled by students marching by the thousands on more than a dozen campuses around the country, showed that months of arrests and government intimidation had failed to stamp out the movement, sparked by the disputed presidential election in June , The New York Times reports.
It was also reported, thousands of members of the pro-government Basij paramilitary organization stormed the grounds of Tehran University on Tuesday and attacked a group of protesting students, several witnesses said, as unrest continued in the capital for a second day following "Student Day" demonstrations Monday.
Armed with steel clubs, electric batons, pepper spray and tear gas, the Basij members first surrounded and later assaulted a group of about 700 students who had gathered in front of the university's technical faculty, where there had also been running battles between the two groups the day before. Regular police units were out in full force in the streets surrounding the university.
"They broke the windows and cut some of us with the pieces of glass," said a student who only gave his first name, Hamed. "We lit fires in front of the faculty's entrance, but they poured in and fights broke out in the hallways," he said in a telephone interview. Hamed said he was wounded on his face in the melee.
Cell phone service in the area was cut, witnesses said. Students fought back, in some cases injuring members of the Basij, who fall under the command of the Revolutionary Guards Corps , The Washington Post reports.
In the meantime, dozens of government agents on motorbikes have surrounded the Tehran office of Mir Hossein Mousavi, the Iranian opposition leader, and the country's chief prosecutor is threatening to arrest him.
The moves come just one day after tens of thousands of students across the country staged the latest in a long series of demonstrations against a government the so-called "Green" movement regards as illegitimate.
Mr Mousavi is the former Prime Minister who was defeated by President Ahmadinejad in an allegedly fraudulent election in June. The regime appears to be stepping up the pressure on him to call off the six months of protests and civil disobedience that have followed.
As Mr Mousavi was holed up at the academy, Iran's chief prosecutor told journalists that he could be charged and hauled before a court. "I declare that from today there will be no tolerance," Gholam Hossein Mohsen said, Times Online reports.