Local authorities in the eastern region are expected to pass laws giving them greater power over the province's finances and security operations if the referendum is passed.

'Serious consequences'

Mario Ayala Ferrufino, permanent secretary of the Supreme National Defence Council, warned on Saturday that the vote was a threat to the territorial integrity of Bolivia.

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Bolivia's Red Ponchos call to arms

The vote could raise "serious consequences for the unity of the country that are in total contradiction" with the constitution, he told the Erbol news agency.

The situation has exposed the divide between the indigenous Indians, who make up 60 percent of the population and largely live in the Andean mountains, and the better-off inhabitants of the lowlands, many of whom have European ancestors.

About 5,000 indigenous Indians held a rally in the city of Santa Cruz on Friday in protest at the referendum.

Fidel Surco, the leader of a powerful indigenous rural group told the crowd at the rally that if violence broke out "the responsibility for a bloodbath" would rest with Santa Cruz's authorities for organising the referendum.

Evo Morales, the country's first indigenous president, has not followed through with a threat to bring troops into the region, but violence between his supporters and those backing autonomy is feared.

'Unconstitutional' poll

Morales has said that he will ignore the result of the vote, calling the move unconstitutional and separatist.

"They're only in it for the money, not for the country. They're only in it to help out a few businessmen, and not the people," he told the Associated Press news agency on Saturday.

Leaders in Santa Cruz want greater autonomy in order to keep more of the province's natural gas revenues and to protect their large plantations and ranches from Morales' plan for land redistribution.

Morales has said that he needs a strong central government to distribute Santa Cruz's wealth to the rest of the country.

On Friday, Morales suggested that the dispute could be decided by a nationwide referendum. However, he also said that some of the state's demands may be worked into Bolivia's new constitution if the referendum is approved.

"If we politicians can't find a way to agree, let the people decide with their vote," he said.

Three others provinces are to hold their own votes on autonomy next month, while two more are considering holding a referendum.