As ministers lay commemorative wreaths at the Czech radio building - which has come to be a symbol of resistance - Czechs at either end of the political spectrum disagree about the value of the 1968 reforms.

Czech radio announces invasion - August 1968

The Czechoslovak Communist Party leader Alexander Dubcek tried to liberalise the country's communist regime by introducing free speech and freedom of assembly.

But the period - that came to be known as the Prague Spring - ended when Warsaw Pact troops invaded on the night of the 20-21 August 1968.

"Our people will never accept this occuption" Czech leaders 1968

More than 100 people were killed, and the Communist leaders, including Alexander Dubcek, were arrested and taken to Moscow.

Despite fierce resistance, a protocol was issued within days of the invasion that banned all parties and organisations which "violated socialist principles".

Paying tribute to '68

On Thursday the Czech President Vaclav Havel said the Prague Spring was "a beautiful time because after 20 years it was possible to breathe and speak freely."

Vaclav Havel:"Anyone who experienced that time will never forget it"

But the former dissident - who led the 1989 peaceful overthrow of the Communist government and was a young playwright in 1968 - also said the Prague Spring was a conflict between two groups of Communists, and "revealed the totalitarian nature of that system."

Helping the wounded during the '68 invasion

When the Social Democrats proposed this week that parliament approve a motion to commemorate the anniversary, a group of right wing deputies opposed it, saying they did not want to voice approval for the Prague Spring.

Those on the left have accused the right-wingers of trying to deliberately discredit the reform efforts of the 1960s for political advantage today.

But in Russia, President Yeltsin described the Prague Spring as an attempt "to escape from ideological dogmatism and lies."