Bolivia's military has re-taken control of the provincial capital of Pando, where 30 have died in clashes between government supporters and opponents.
Bolivia's President Evo Morales has begun talks with a key opposition leader, after days of clashes between pro- and anti-government supporters.
Defence Minister Walker San Miguel said a relative calm had been restored to Cobija, two days after the government declared a state of emergency there.
Mr Morales is meeting Mario Cossio - the governor of Tarija region - to try to ease tension in energy-rich eastern provinces held by the opposition.
The opposition wants President Evo Morales to postpone a referendum on a new constitution, due in December.
The talks come after 30 people were killed in the region of Pando.
The ongoing crisis will be the focus of an emergency regional summit on Monday.
The crisis centres on Mr Morales' decision to hold a referendum on a new constitution in December.
Chilean President Michelle Bachelet said she hoped the Union of South American Nations (Unasur) could help promote a democratic solution.
The president says he wants to re-distribute Bolivia's wealth and give a greater voice to the large indigenous community.
"We cannot be idle in the face of the situation, provoking anxiety among us," she said.
Opposition leaders oppose the plan and demand greater autonomy as well as more control over revenues of natural gas in their areas.
The crisis has arisen over plans by President Morales to re-distribute the country's wealth and give a greater voice to the large indigenous community.
The talks between President Morales and Mr Cossio are being held at the presidential palace in La Paz, officials say.
It later escalated when Mr Morales expelled the US ambassador to Bolivia, Philip Goldberg, accusing him of stoking anti-government sentiment.
Before the meeting, Mr Cossio said the onus was now on Mr Morales to make concessions so that further violence could be averted.
Speaking prior to leaving the country on Sunday, Mr Goldberg rejected the accusations and said the expulsion was a grave error.
Earlier, one of the opposition leaders has ordered the lifting of his supporters' widespread roadblocks in Santa Cruz province, which have left the energy-rich area short of gas, oil and food.
"The decision can have many serious effects and it seems that so far this hasn't been evaluated," he warned.
Branko Marinkovic said the move was a "sign of good will" which could foster dialogue and prevent any more blood being spilled.
'Killed like pigs'
In a separate development, the military on Sunday re-took control of Pando's provincial capital, Cobija, two days after the government declared a state of emergency there.
Bolivia's defence minister said troops regained control of Cobija in the northern jungle province of Pando early on Sunday.
Defence Minister Walker San Miguel said a relative calm had been restored to Cobija.
Witnesses said the small city was quiet at midday with shops closed and government forces guarding its airfield and a military barracks.
US envoy expelled
One opposition leader has ordered the lifting of its roadblocks in Santa Cruz
The troops also continued to find bodies from a "massacre" of pro-government farm workers on Thursday, in which officials said nearly 30 people were killed.
The troops also continued to find bodies from a "massacre" of pro-government farm workers on Thursday, in which officials said nearly 30 people were killed.
The decision can have many serious effects and it seems that so far this hasn't been evaluated Philip GoldbergExpelled US Ambassador to Bolivia In Bolivia's opposition heartland
On Saturday, President Morales ordered the arrest of Pando Governor Leopoldo Fernandez for allegedly orchestrating the attack, saying he had hired "Brazilian and Peruvian assassins" to carry out the "ambush".
On Saturday, President Morales ordered the arrest of Pando Governor Leopoldo Fernandez for allegedly orchestrating the attack, saying he had hired "Brazilian and Peruvian assassins" to carry out the "ambush".
Mr Fernandez has denied having anything to do with the deaths, insisting they were the result of clashes between rival groups.
Mr Fernandez has denied having anything to do with the deaths, insisting they were the result of clashes between rival groups.
The government has a great ability to distort things, and its arguments are always the same - accusations without reason Pando Governor Leopoldo Fernandez
The ongoing crisis will be the focus of an emergency regional summit on Monday.
Another two people were killed on Friday at Pando's main airfield as government troops opened fire to disperse opposition protesters.
Chilean President Michelle Bachelet said she hoped the Union of South American Nations (Unasur) could help promote a democratic solution.
One of the opposition leaders has meanwhile ordered the lifting of his supporters' widespread roadblocks in eastern Santa Cruz province, which have left the energy-rich area short of gas, oil and food.
"We cannot be idle in the face of the situation, provoking anxiety among us," she said.
Branko Marinkovic said the move was a "sign of good will" which could foster dialogue and prevent any more blood being spilled.
The Bolivian crisis escalated when Mr Morales expelled the US ambassador to La Paz, Philip Goldberg, accusing him of stoking anti-government sentiment.
"We hope the government will also signal good will by ending this repression and genocide in the province of Pando," he added.
Mr Goldberg has rejected the accusations, saying the expulsion was a grave error.
The BBC's Andres Schipani in Santa Cruz says Mr Marinkovic is considered by many to be the soul of Bolivia's radical opposition.
Talks continue
The announcement by Mr Marinkovic came ahead of a meeting in La Paz aimed at easing the tension between President Morales and a representative of the opposition, Tarija Governor Mario Cossio.
President Morales has said he is determined to continue talks to end the violence, but also vowed not to change his referendum plans.
Both the government and the opposition have appealed for calm
Opposition leaders have meanwhile insisted that they will pull out if just one of their supporters is killed as government forces try to re-establish control in a number of eastern cities.
Both sides held negotiations in the capital overnight on Saturday in an effort to end the crisis. Earlier reports said they had reached a basic agreement.
Before last week's violence, opposition groups had demanded the government cancel a constitutional referendum on 7 December that would give more power to indigenous and poor communities by carrying out land reform and redistributing gas revenues.
They and their supporters instead want greater autonomy as well as more control over revenues of natural gas in their areas.
Mr Morales, Bolivia's first indigenous president, has denounced the leaders of the opposition as fascist and racist elements that are determined to overthrow him.
