Police detained more than 400 people near the grave of a student who burned himself to death 20 years ago to protest the Soviet-led invasion that crushed "Prague Spring" reforms, activists said.

The police action capped Czechoslovakia's most serious week of political unrest since Jan Palach set himself ablaze in central Wenceslas Square in January 1969 and thousands of people took to the streets in shock and grief.Former Communist Party chief Alexander Dubcek was quoted Sunday as saying the young people now demonstrating against Communist authorities are frustrated by a political and economic system that offers them no future.