Mousavi supporters clash with police in Tehran

TEHRAN (Reuters) - 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, witnesses said.

A reformist website, Mowjcamp, said police opened fire on protesters at Haft-e Tir square, but there was no independent confirmation. "Some people were injured," Mowjcamp reported.

Thousands of Iranian security forces had assembled on the streets of Tehran to prevent any opposition gathering.

"Police clashed with hundreds of protesters. They were chanting 'Death to dictators'. Police used batons to disperse them," a witness said.

Another witness said police fired teargas at the crowd and arrested at least five protesters.

"There are hundreds, chanting 'God is greatest'. Police and Basij militia are outnumbering the protesters," one witness said.

"Hundreds of police, riot police, Basij militia and plainclothes are in the main squares," another said. "Police cars with black curtains have been parked in the squares to take away protesters."

Iran's Revolutionary Guards and its allied Basij militia have warned the opposition to avoid using any anti-U.S. rally to revive protests against the clerical establishment after June's disputed presidential election in which Mahmoud Ahmadinejad won a second term.

Opposition leaders Mousavi and Mehdi Karoubi, who both ran against Ahmadinejad, had urged their supporters to take to the streets to protest against his government.

Karoubi joined the protest on Wednesday, Mowjcamp said: "He is walking toward the former American embassy."

Iranian militants stormed the embassy on November 4, 1979 and held 52 Americans hostage for 444 days.

Anti-Western rallies usually take place outside the old U.S. embassy -- now called the "den of espionage" in Iran -- to mark the anniversary of the day in 1979 that the embassy was seized.

Some reformist websites called on people to gather outside the Russian embassy, in an apparent protest at Moscow's recognition of Ahmadinejad's re-election on June 12.

"Dozens of police and Basij forces are around the Russian embassy as well," one witness said.

Another witness said dozens of police were walking around the British embassy in central Tehran.

The unrest after the election in June has been the worst in Iran in the past three decades. In September, opposition demonstrators clashed with government backers and police at annual pro-Palestinian rallies.

The authorities deny vote-rigging and have portrayed the unrest as a foreign-backed bid to undermine the Islamic state.

(Writing by Parisa Hafezi; editing by Mark Trevelyan)