(Updates with end of summit)

By Pav Jordan

SANTIAGO, Sept 15 (Reuters) - South American leaders fully backed Bolivian President Evo Morales on Monday and called on rebel governors in the country's eastern provinces to cease violent protests against his socialist policies.

Nine presidents from the region, who met for six hours in Chile's capital, also condemned any attempt at a coup in the impoverished country and called for an investigation into an alleged massacre of Morales supporters in one province.

At least 16 people died in Bolivia in the past week as supporters of Morales clashed with rightist opponents angered at his attempts to give Indians more political power and redistribute land to the poor.

"We ratify our full support for the democratic government of President Evo Morales. At the same time, groups must end illegal occupations of buildings and blockades as a condition for talks," Argentine President Cristina Fernandez said after the meeting.

The leaders encouraged both sides to negotiate an end to Bolivia's deep political crisis, which disrupted natural gas supplies to its large neighbors Argentina and Brazil.

In last week's demonstrations, anti-Morales groups sabotaged natural gas pipelines and plundered and occupied public buildings throughout the east.

"We hope opposition groups can understand this statement as being from all of South America, not just its presidents," Morales said after the summit in Santiago, which he attended.

Before heading to Chile, Morales and the opposition met to discuss potential steps to halt the deadly political unrest. Talks between the governors and the Bolivian vice president continued while Morales was at the summit.

Perennially unstable Bolivia has massive natural gas reserves that are crucial to development in the region and neighbors are keen to preserve the Morales presidency.

Morales, Bolivia's first Indian president, is highly popular but his drive for deep socialist reforms such as land redistribution has polarized the country.

Among those attending the summit were key Bolivia ally President Hugo Chavez of Venezuela, who is stridently anti-Washington, and Brazil's President Luiz Inacio Lula da Silva, a moderate leftist who leads the region's biggest economy and Bolivia's top foreign investor.

Morales and Chavez expelled the U.S. ambassadors in their countries last week, saying they were backing the Bolivian opposition movement.

DIVIDED

Bolivia is divided over a constitution Morales is trying to push through. Conflict between both sides deepened after Morales and the governors were all strongly endorsed in an August recall vote.

Morales' reforms have drawn fierce opposition in lowland regions in the east of the country, which want greater autonomy from the central government in highland La Paz and a bigger share of energy resources.

The army has arrested 10 people accused of organizing anti-government protests in Cobija, the capital of sparsely populated Pando province in the Amazon near Brazil.

The government declared martial law in the province on Friday, saying opposition groups had massacred pro-Morales peasants. Officials have said 16 to 28 people died in that incident in rural Pando, as well as two more in Cobija.

An official said he regretted contradictions on the death toll and would not give out a new figure until it is certain.

In the opposition stronghold of Santa Cruz in eastern Bolivia, the opposition lifted roadblocks that had crippled the city to help foster talks. It was not clear whether supporters of Morales would lift their blockades. (Additional reporting by Antonio de la Jara and Rodrigo Martinez in Santiago and Eduardo Garcia in La Paz; Editing by Fiona Ortiz and John O'Callaghan)

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