Police have entered al-Azhar University in the Egyptian capital Cairo to disperse students protesting in support of ousted President Mohamed Morsi.
The interior ministry said it had responded to a request for help from university authorities.
Pro-Morsi students had been holding protests at the campus for weeks.
The operation come hours after the arrest of Essam al-Erian, a senior leader in the Muslim Brotherhood movement to which Mr Morsi belongs.
Mr Erian is vice chairman of the Freedom and Justice Party (FJP), the Brotherhood's political wing. Prosecutors had ordered his arrest in July, after the military ousted Mr Morsi.
Officials at al-Azhar were quoted by local media as saying that the protesting students had ransacked university offices before the police intervention.
Photos from the scene showed damage to the buildings and anti-military graffiti sprayed on the university's walls.
The interior ministry said in a statement that the action was taken to "protect lives and public property".
There were reports that some of the students had been arrested, although it was not clear how many.
Protester Mahmoud Salah, said authorities had planted troublemakers among the students to stir the violence.
"Our protests are peaceful. We are against the coup," Mr Salah told The Associated Press.
Tension at the university campus has been building for weeks, with students protesting against the military-backed government that replaced Mr Morsi and against the university leadership itself.
Ahmed Al-Tayeb, the Grand Sheikh of Al-Azhar, regarded as one of the most prestigious seats of learning in Sunni Islam, gave his backing to the removal of Mr Morsi.
Although the latest moves come as the interim government continues a crackdown against the Islamist movement, students at al-Azhar have also had other grievances against the university's management.
In April, hundreds of students broke into Mr Tayeb's offices in a protest sparked by an outbreak of food poisoning at the campus that left 500 students in hospital.