The Iranian authorities have arrested scores of what it describes as "thugs and ruffians" following four nights of civil unrest in the capital Tehran, state-run radio reports.
Some students were attacked with knives
Riot police were called in to break up clashes between supporters and opponents of clerical rule near Tehran university in the early hours of Saturday morning.
State-run radio said those detained included some who had entered and damaged a student dormitory - a reference to militants loyal to the country's supreme religious leader, Ayatollah Ali Khamenei.
Police have issued a warrant for the arrest of Sa'id Askari, a prominent pro-government vigilante leader who was seen at the demonstrations.
The protests, which are now reported to have spread to other cities, have been against the conservative clerical establishment and the reformist President, Mohamed Khatami, who is accused of betraying hopes for change.
Latest reports from Tehran say that thousands of protesters have returned to the streets for a fifth consecutive night, but that a huge security operation has dampened the noisy demonstrations of previous nights.
The US has denounced action against the student-led protests and called on the Iranian Government to protect demonstrators' rights.
The authorities have accused the US and Iranian exiles of fomenting the unrest.
Friday night saw security forces and hundreds of vigilantes used tear gas, clubs, chains and iron bars to disperse protesters.
Students said dozens of armed Islamic vigilantes also attacked students sleeping in their rooms.
Khamenei has warned students to stop the protests
"Suddenly we heard windows being smashed," a student told the Associated Press news agency.
"Fists and kicks by hardline vigilantes woke up some of the students."
A statement by the hardline judiciary said most of those arrested after the dormitory raid were "thugs and ruffians with criminal records".
The BBC's Miranda Eeles, in Tehran, says thousands of ordinary Iranians have joined the students in demonstrations.
Despite the rough treatment of protesters, and the warnings from Ayatollah Khamenei, our correspondent says the demonstrators' resolve to continue speaking out against the slow process of reform shows no sign of waning.
Student associations have said they will continue to demonstrate until 9 July, to commemorate the violent attack by hardline groups on students four years ago.
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