They said a number of people who had tried to reach the central Tehran dormitories -- the focal point of the protest movement -- were dragged from their vehicles and taken away by police.

Several people who honked their car horns to show support for the protestors were also seen being dragged from behind the wheel and beaten up.

All roads surrounding the Amir Abad dormitory facility were sealed off to traffic by hundreds of police and anti-riot troops, while the student compound itself was also under guard.

Police also took up positions inside the dormitory area, although they were unarmed and only carrying walkie-talkies.

The student news agency ISNA said the order to deploy on campus was issued by Iran's Supreme Council of National Security, the Islamic republic's top decision-making body on security issues.

The agency said the body had ordered "police to assure security inside and outside the university campus".

The decision to deploy forces inside the university grounds appeared to be aimed at both preventing renewed protests and probable clashes between students and members of pro-regime vigilante groups, notably the Ansar Hezbollah militia and the volunteer Basij movement.

Overnight Thursday there were several hours of clashes in which about 40 students were injured and 10 others arrested.

The protests have taken on a particularly virulent tone, with the crowds shouting slogans hostile to Iran's supreme leader, Ayatollah Ali Khamenei, including "Death to the dictator" and "Khamenei, step down from the throne."

Iran's clerical leadership has accused the United States of orchestrating the unrest.