Giving the weekly Friday prayer sermon, Ayatollah Hassan Taheri-Khoramabadi said "opportunist elements" backed by "foreign enemies" had provoked the unrest that left at least two people dead.

"The US will not tolerate a solid and stable Islamic regime in the world. By provoking the disturbances it was trying to tell other nations not to have good relations with Iran," he said in an address from Tehran University, the scene of the most serious protests.

In response to rumours of another student demonstration planned for Tehran on Saturday, Iranian Interior Minister Abdolvahed Musavi-Lari said that nobody had sought permission for a rally.

"Up to now no-one has asked for any permission and we haven't granted any," he told Iranian TV, during a visit to Tehran University.

Arrests and punishment

Iranian authorities have been making extensive efforts to arrest and punish the activists they suspect of being behind the recent unrest.

Units of the Revolutionary Guards and the Basij Islamic militia have been deployed in sensitive areas in the capital, including near Tehran University.

Hundreds of arrests have taken place since students from the university took to the streets last week, according to the human rights group Amnesty International.

Amnesty also says it has reports that at least five people have been killed, and dozens injured, while many well-known student activists are reported to have gone into hiding.

The Iranian authorities have confirmed two deaths during the unrest.

In a massive official rally on Wednesday, hundreds of thousands of supporters of Iran's hardline Islamic rulers reclaimed the streets of the capital from the reform movement, in a massive official rally.

Deputy Parliamentary Speaker Hasan Rowhani told the crowd that those arrested for sabotage and destroying state property during the student protests would face the death penalty.

Iran's elected president, Mohammad Khatami, who shares many of the students' aims, condemned the violence, which broke out on Monday and Tuesday after four days of mainly peaceful demonstrations.

(Click here to see a map of Tehran showing the demonstration area)

On Tuesday, demonstrators and security forces fought running street battles in several parts of Tehran, a day after the city's governor banned demonstrations and after Mr Khatami said they should stop.

The unrest began after the closure of the liberal Salam newspaper last week and the introduction of new legislation to curb Iran's free press.

Newspapers have enjoyed relative freedom since the president's election in 1997, but have come under mounting pressure from hardliners in recent months.