A satellite TV run by exiles in the US
urged people to join the protest
Shortly before midnight on Tuesday, hundreds of students gathered near Tehran University chanting slogans against the country’s ruling clerics, Aljazeera's correspondent said.
The protest swelled to thousands of demonstrators before riot police and members of the Basij volunteer forces, who perceive themselves as defenders of Iran’s 1979 Islamic Revolution, intervened. One witness said tear gas was also used to break up the protest.
Demonstrators left smashed windows, damaged public telephones and burnt vehicles. The student news agency ISNA quoted Intelligence Minister Ali Yunesi as saying 80 students were arrested.
Yunesi, who said the demonstrators were shouting "illegal slogans", said the protest was "organised by foreign media and satellite television channels".
He was referring to a US-based Iranian exile station that urged people to go to the campus after students demonstrated there earlier on Tuesday.
Following the protest, Basij members patrolled the capital’s streets armed with light weapons.
Meanwhile, eight members of the Ansar Hizb Allah group, including a local leader, were arrested in the north-eastern city of Mashhad for attacking a student gathering, said press reports.
The group allegedly attacked students protesting against an Ansar assault the previous week, said the Tosseh newspaper.
Leaders urge unity
Wednesday's protest came in the run-up to the anniversary of clashes in July 1999. During the overnight protest Ali Taala, a Director of Political and Security Affairs in Tehran, was quoted by ISNA as calling on demonstrators to avoid a repeat of the 1999 events.
Iran’s Spiritual leader Ayatollah Ali Khamenei called on students over the weekend to “maintain their calm” in order to foil, what he said was, a US plot to destabilise the Islamic state.
He urged Iranians to remain unified. Khamenei’s comments came after US Secretary of State Colin Powell called on Iranians to pressure their political and religious leaders.
The last major student protest was in 2002, when thousands of people rallied against a death sentence handed down to Hashem Aghajari, a university professor, who was accused of blasphemy.
He remains in jail and his sentence is still under review.
Meanwhile, Washington stepped up its rhetoric against Iran. US Defence Secretary Donald Rumsfeld accused Tehran of developing a nuclear weapons programme.
Speaking during a brief visit to Germany, Rumsfeld claimed Tehran would "soon" possess nuclear arms. Iran strongly denies the allegations.
In recent weeks, Washington has increasingly accused Tehran on a number of issues including allegedly interfering in neighbouring Iraq .