They told local radio they plan to seize control of the operations of Brazil's state energy firm Petrobras, France's Total and Spain's Repsol YPF in the Chaco region of eastern Bolivia.

Wilson Changaray, head of the Guarani People's Assembly, said: "Today we are going to occupy production fields and we are going to paralyse all oil [and gas] activities and suspend exports to Brazil."

Earlier this month, Guarani Indians took over a control station on the Transierra pipeline that transports 60 per cent of the gas Bolivia exports to Brazil, its biggest customer.

Jorge Boland, trader manager of Transierra (a Petrobras, Total and Repsol YPF joint venture), said supplies were normal and played down the risk of disruption.

Boland said: "It is possible [a disruption], but ever since they invaded the control station on August 15, they've been saying this ... but nothing has been disrupted."

Payment dispute

The Indians say Transierra has not fulfilled a promise to invest $9million in development projects in the area.

Boland said the new threat came after Transierra formally refused to make a one-off payment of $9million for development projects in the area instead of constant regular payments over 20 years as agreed earlier.

He said: "Under the deal we invest $450,000 a year in works ... we do not agree to pay everything at once."

Boland said that Transierra was trying to set a meeting with the Indians for Tuesday or Wednesday.

He said a meeting last Friday was cancelled because of security concerns as it was on Guarani territory.

Changaray said the Indians had decided to step up protests against Transierra because company directors had failed to attend the meeting.

Changaray said: "We are not asking for an economic handout, but for compensation for all the wealth that they extract from our land and the damage they leave behind."

Huge reserves

Bolivia sits on the second-largest natural gas reserves in South America after Venezuela.

The threat is the latest drawback for Petrobras in Bolivia, which supplies about half of Brazil's increasing natural gas consumption.

Brazil imports about 26 million cubic metres a day from Bolivia, roughly half of what it consumes.

The government of Evo Morales nationalised Bolivia's energy sector on May 1, and has since been seeking to raise prices on gas exports to Brazil by as much as 75 per cent.