Opposition leaders were attacked and security forces flooded the streets of Iran's major cities on Thursday as the authorities put down protests they feared would mar rallies to celebrate the 31st anniversary of the Islamic Republic.

The three men who have become unofficial leaders of the "Green" opposition movement all faced off against police and plain-clothes government security forces as they tried to join government rallies.

There were contradictory reports as to whether Mir Hossein Moussavi, a defeated candidate in last year's presidential election, succeeded in getting through. But cars carrying another reformist candidate, Mehdi Karroubi, and a former president, Mohammad Khatami, were seen being surrounded by plain-clothed security forces....

The government rallies, an annual highlight usually marked by defiant speeches and calls of "Death to America" from huge crowds, commemorate the anniversary of the return of Ayatollah Khomeini from exile in 1979 and the subsequent flight of the Shah.

Government news agencies said tens of millions of people attended in cities across the country. Television pictures showed huge crowds in Freedom Square in Tehran. Opposition activists based abroad said they had been paid to attend, and given food.

In a lengthy speech, President Mahmoud Ahmadinejad told them that criticism of the regime from the West was because of its fear of Iran's "greatness and glory".

The government had been warning for days that no dissent would be tolerated....