Iranian police clashed on Wednesday with supporters of Iran's opposition leader Mirhossein Mousavi in the capital Tehran as the country marked the 30th anniversary of the storming of the US embassy.   

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. Some protesters were arrested. 'Police clashed and arrested at least five protesters,' one witness said.

Opposition leaders Mousavi and Mehdi Karoubi had urged their supporters to take to the streets to protest against President Mahmoud Ahmadinejad's government.

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

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

The unrest after the vote was the worst in Iran in the past three decades.

'Hundreds of police, riot police, Basij militia and plainclothes are in the main squares,' another witness said.

'Police cars with black curtains have been parked in the squares to take away protesters.'    

Another witness also said dozens of police were walking around the British embassy in central Tehran. 'Dozens of police and Basij forces are around the Russian embassy as well,' the witness said.

Some reformist websites have 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.

Anti-Western rallies usually take place outside the old US embassy -- now called the 'den of espionage' in Iran -- to mark the anniversary.

Iranian militants stormed the embassy on Nov. 4 1979 and held 52 Americans hostage for 444 days. 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. - Reuters