Security forces and hardline supporters of Iran's conservative leadership have clashed with large crowds in the capital Tehran who were protesting against clerical rule.
It was the fourth night of protests
Tear gas, clubs, and iron bars were used to disperse the protesters.
Hardline vigilantes were seen pulling people from cars and beating them. Gunfire was also heard.
Saturday morning's demonstrations were the fourth consecutive night of protests about the slow pace of reform in the country.
The Iranian supreme leader, Ayatollah Ali Khamenei, had warned demonstrators they would be shown no pity if they continued their protests.
Despite attempts by the security forces to seal off the area, roads near Tehran University were clogged with cars and protesters on foot, hooting horns and shouting slogans.
Stones were thrown and chants wishing death on Ayatollah Khamenei were heard.
Such condemnation of the supreme leader is said by correspondents to be unprecedented in Iran.
Eyewitnesses said some police officers stood by as militiamen beat the protesters.
"Most were armed with sticks and chains but a few had
Kalashnikovs," a Reuters correspondent reported from the scene.
The authorities have accused the United States and Iranian exiles of fomenting the unrest.
Exiled opposition groups have been encouraging the protests through US-based satellite channels.
'Freedom and democracy'
Uniformed and plainclothes officers saturated the city on Friday, stopping and searching vehicles in the area after three nights of street protests.
During clashes with police on Thursday night, 40 students were injured and 10 arrested.
The unrest, which began with protests at plans to privatise the university, has grown into open condemnation of both Ayatollah Khamenei and President Mohammad Khatami, who was elected on a reformist platform.
Students have been heard chanting "freedom" and "democracy" and calling for Ayatollah Khamenei to be hanged.
But one senior cleric, former President Akbar Hashemi Rafsanjani, said at Friday prayers that the US was trying to "snare" Iran's young people.
Fear at the top
The authorities are anxious for the situation not to get out of hand.
They have stressed to students that they will not tolerate a repeat of the events of 1999, when clashes with law-enforcement officers lasted for three days and left at least one student dead.
Those anti-government protests were the most serious since the fall of the Shah in 1979.
About 70% of Iran's 65 million population is under 30, and has little or no memory of the late Ayatollah Khomeini's Islamic revolution.
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