TEHRAN Police clashed with supporters of Iran's opposition leader Mirhossein Mousavi in Tehran on Wednesday when a rally marking the 30th anniversary of the storming of the U.S. embassy turned violent.
Reformist website Mowjcamp said police opened fire on protesters at Haft-e Tir square but there was no independent confirmation of the report.
"Some people were injured," Mowjcamp said, reporting other protests in the cities of Shiraz and Rasht.
Iran's Revolutionary Guards and the allied Basij militia had warned the opposition not to try to hijack an annual anti-U.S. rally to revive protests against the clerical establishment after June's disputed presidential election.
"Police clashed with hundreds of protesters. They were chanting: 'Death to dictators'. Police used batons to disperse them," a witness said. People traditionally chant, "Death to America" at the annual state-organized rally.
By evening the crowds had dispersed but police and Basij maintained patrols on the streets. Mowjcamp reported the arrest of at least 23 protesters in Tehran and the northern city of Rasht by Iran's security forces.
The crackdown showed no compromise from the leadership, underlined by Supreme Leader Ayatollah Ali Khamenei's recent comment that it was a crime to question the June 12 vote which secured the re-election of President Mahmoud Ahmadinejad.
Defeated presidential candidates Mousavi and Mehdi Karoubi, who are committed to reform, had urged supporters to take to the streets on Wednesday to protest against the government despite warnings from the security forces about "illegal gatherings."
Karoubi, who joined the protests on Wednesday, was attacked by plainclothes officers, his website Tagheer said. One of his bodyguards was hospitalized it said but gave no further details.
Police fired teargas at the crowd and arrested at least five protesters, one witness said. Mobile phone networks were shut down to try to prevent protesters from organizing while Basij militia on motorbikes drove at crowds and used batons.
"There are hundreds, chanting 'God is greatest'. Police and Basij militia are outnumbering the protesters," one witness said.
Another witness said hundreds of police, Basij militia and plainclothes officers are in the main squares.
The turmoil after the June vote was the worst in Iran since protests which led to the overthrow of the U.S.-backed Shah three decades ago. Authorities denied rigging the vote and portrayed the unrest as a foreign-backed bid to undermine the Islamic state.
Street protests have also exposed serious rifts over reform in the clerical leadership, already under international pressure over its nuclear program.
Washington fears Iran is seeking a nuclear bomb and has threatened more sanctions through the United Nations. Tehran says its nuclear program aims to generate electricity.
Thousands of people gathered in front of the former U.S. embassy for the latest state-organized rally where influential lawmaker Gholamali Haddadadel criticized the opposition leaders.
"I don't know how they are going to answer to the great Iranian nation. They claim they are followers of the revolution but issue statements that are in the interests of Iran's enemies," he said in a speech.
Haddadadel said the U.S. administration should change its policy toward Iran's nuclear energy program.
U.S. President Barack Obama used the anniversary of the hostage crisis to urge Tehran to make concessions over its nuclear program, saying it needs to turn the page on the past and forge a new relationship with the United States.
"Iran must choose," Obama said. "We have heard for 30 years what the Iranian government is against; the question, now, is what kind of future it is for."
French Foreign Minister Bernard Kouchner said his government was worried by the police crackdown and the situation in Tehran was dangerous.
"None of this bodes well. I hope that I am wrong, but a government that represses its people at home and refuses dialogue abroad does not bode well," Kouchner said in Paris.
The nuclear question and relations with the West have also caused deep divisions alongside the political furor.
"There is real domestic turmoil in Iran," said Mark Fitzpatrick of London's International Institute for Strategic Studies.
Protesters at the official rally carried banners saying "We are ready to sacrifice our blood for Khamenei," and "Death to America" and "Death to Israel" before they dispersed.
Anti-Western rallies take place annually outside the embassy -- now called the "den of espionage" in Iran -- to mark the anniversary of the day in 1979 that the building was seized.
The militants held 52 Americans hostage for 444 days.
Protesters also targeted the Russian embassy in Tehran, where they chanted "The Russian embassy is a den of spies" and "Death to Russia."