Tight security in Iran ahead of anti-U.S. rally

TEHRAN (Reuters) - Hundreds of Iranian security forces were on the streets of Tehran on Wednesday to prevent any gathering by the opposition when the country marks the 30th anniversary of the storming of the U.S. embassy.

Opposition leaders Mirhossein Mousavi and Mehdi Karoubi have urged their supporters to take to the streets to stage protests against the government of President Mahmoud Ahmadinejad.

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.

The unrest that erupted 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," a witness said.

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

Another witness 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.