Thousands of people retraced the paths of a student demonstration 20 years earlier in Prague on November 17 to mark the 20th anniversary of the collapse of communist rule in the former Czechoslovakia.

On the night of November 17 1989 about 15 000 students were challenged by riot police in Prague, demanding an end to decades of communist rule. Inspired by the collapse of the Berlin Wall the previous week, the demonstrators' actions were dubbed the "Velvet Revolution" because participants wanted to overthrow the regime peacefully.

Demonstrators, on that occasion 20 years ago, had found themselves cornered and attacked by hundreds of riot police. The savage assault, which left scores injured, galvanised the Czech people and triggered further mass demonstrations.

Later, on November 25 an estimated 800 000 protesters poured onto Prague's streets in a massive show of defiance against a government that had little authority over its people by that stage.

Czech police eventually had to abandon the fight to contain the unrest when it was clear that brute force was proving ineffective.

The Communist Party leadership resigned and dissident writer Vaclav Havel, who had spent years in prison, emerged as president on December 29 1989.

Speaking at a commemorative gathering at the Czech Senate, Havel, now 73, urged Czechs not to forget those involved in the country's battle for freedom. He also took advantage of the occasion to criticise what he saw as new forms of authoritarianism hiding behind a democratic facade, interpreted as an attack on Russia.

"The era of dictatorships and totalitarian systems has not ended at all," he said. "It may have ended in a traditional form as we know it from the 20th century, but new, far more sophisticated ways of controlling society are being born. It requires alertness, carefulness, caution, study and a detached view."