Chile has called an emergency meeting of the Union of South American Nations to help resolve the crisis in Bolivia.
Chilean President Michelle Bachelet said the meeting - on Monday - might help promote a democratic solution.
President Evo Morales imposed martial law in the northern region of Pando on Friday, after clashes between opponents and supporters of the government.
The crisis has arisen over a plan by the Bolivian president to hold a referendum on a new constitution.
The turmoil escalated when President Morales expelled the US ambassador from Bolivia, accusing him of stoking anti-government sentiment.
Protesters have attacked gas supplies to neighbouring Brazil and Argentina.
The BBC's Daniel Schweimler in the eastern city of Santa Cruz - an opposition stronghold - says no-one wants to see a tense situation spiral out of control.
Secret meeting
At least 16 people have been killed in Pando in recent days.
President Morales accused the region's governor of hiring foreign hitmen to attack his peasant supporters.
The governor, Leopoldo Fernandez, who rejects the claims, is reported to have fled to neighbouring Brazil.
The president has said that martial law is not needed elsewhere in the country.
Both the government and the opposition have called for an end to the violence.
The government representative in Santa Cruz, Gabriela Montanyo, concerned about her safety, would only agree to meet the BBC at a secret location, our correspondent says.
The president wants to give more power to indigenous and poor communities, by carrying out land reform and redistributing gas revenues.
Mr Morales's attempts to change the constitution are fiercely opposed by opposition governors who run five of Bolivia's nine regions.
They and their supporters want greater autonomy as well as more control over revenues of natural gas in their areas.
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