At least 10,000 students marched through the centre of Tehran on the fifth day of protests against press censorship and police brutality, their anger swelled by last Friday's police raid on the campus that left one dead and many in hospital. "We don't want a government of force, we don't want a mercenary police," they chanted.
But police in the city centre fired tear gas and shots into the air to disperse the crowd, bundling several protesters into vans. Shop owners hurriedly pulled down their shutters amid fears of a pitched battle in the heart of the commercial district.
An explosion from a hand grenade, apparently thrown from a passing motorcycle, caused panic and sent thousands of protesters streaming back on to the campus. Thousands more students joined academic staff in a peaceful sit-in protest against the police raid.
Tehran journalists, however, looked likely to abandon a planned one- day strike in support of the banned reformist newspaper Salam, after the paper's publisher urged colleagues from 20 other media outlets not to contribute unwittingly to an information blockade.
Behind the student grievances lies a yawning divide between reformists supporting President Mohammad Khatami and the conservative religious establishment, backed by the country's religious leader, Ayatollah Ali Khamenei.
The President has condemned the assault on the university, but he may also feel embarrassed by the stridency of the student demands, which include calls for the dismissal, and even execution, of the country's police chief, General Hedayat Lotfian.
The students have ignored a ban by the National Security Council, which the President chairs, on further protests without authorisation. Instead, some demanded that the President come out and address the rally, shouting: "Khatami, where are you? Your students have been killed."
The protests have pushed the conservatives on to the defensive and yesterday Ayatollah Khamenei joined the chorus of condemnation of last Friday's police raid. It had "pained his heart", he said.
But in Iran's increasingly polarised atmosphere his regrets fell on deaf ears and condolences from the Ayatollah to the students were booed when his message was read out at the demonstration.
On Sunday Iran dismissed two security chiefs responsible for the raid, though there has been no action taken against General Lotfian.
The crisis started in 1997 when Mr Khatami was elected by a big majority on a reformist ticket, dealing a setback to the conservatives and their clerical allies.
The latest round started only last week when government hardliners pushed through a new law increasing censorship of the press. The law was seen as an attack on the President, as the country's independent media is overwhelmingly pro-Khatami.
The scale of the reaction has demonstrated the extent of popular alienation, especially among the young, towards the conservative religious establishment.Reuse content