By Daniel Schweimler BBC Havana correspondent

The people of Cuba are being asked to vote over the next three-and-a-half days on an amendment to the country's constitution that would declare their political and economic systems to be untouchable.

Castro called Bush 'liberator who nobody invited'

More than 129,000 voting stations have been set up in just a few days.

The referendum comes three days after President Castro brought millions of people out onto the streets as part of a campaign to counter growing calls for democratic reforms to Cuba's communist government.

When faced with difficulties, few are better than President Fidel Castro at mobilising his people - he said 86% of the population participated in rallies across the country on Wednesday.

'Resounding endorsement'

Now, the Cuban people are being asked to ratify an amendment agreed earlier in the week.

The move is a response to growing calls from both inside and outside Cuba for President Castro to initiate democratic reform.

Cuban dissidents have presented an 11,000-name petition to the National Assembly calling for greater civil liberties.

Cuban officials have said it has little chance of success.

Those dissidents have said that the Cuban Government's response shows that it is scared of the growing calls for change.

And outside Cuba, US President George Bush said that Washington would not lift its 40-year trade embargo and travel ban until it saw fundamental democratic reforms on the island.

Announcing the referendum, President Castro urged the Cuban people to give Mr Bush - who he called "his liberator who nobody invited" - a strong and worthy response.

President Castro said the voting was being organised by social groups and was not a state activity.

But nearly all social groups in Cuba are closely linked to the state.

And there is little doubt that the vote will see a huge turnout, a resounding endorsement of the Cuban Government and political system and a strong but predictable condemnation from Fidel Castro's enemies in Washington and Miami.