Updated

South American presidents met urgently Monday hoping to prevent a political collapse in Bolivia, where the government planned to charge a rebellious eastern governor with genocide for allegedly ordering the machine-gunning of peasants.

Bolivia's leftist president, Evo Morales, arrived at the hastily called summit having effectively lost control of half of his country. Anti-Morales protesters have blocked highways, taken over national government offices, closed border crossings and sabotaged pipelines, briefly forcing a cutoff of nearly half of Bolivia's natural gas exports to Brazil.

The most serious challenge yet to Morales' presidency is being spurred by governors of Bolivia's autonomy-seeking lowland provinces, home to the nation's energy deposits and best farmland.

"I've come here to explain to the presidents of South America" that these governors have attempted a coup, Morales said. He accused them of "inciting crimes against humanity by groups massacring the poorest of my country."

The governors want a larger share of the nation's gas profits, and are demanding that Morales cancel the centerpiece of his 3-year tenure: a planned referendum on a new constitution that would give Bolivia's long-suppressed indigenous majority more power, let Morales run for a consecutive second term and transfer fallow terrain to landless peasants.

Morales has the support of most Bolivians — voters ratified his presidency by an impressive 67 percent in an Aug. 10 recall referendum — a 13 percent jump over what the native Aymara and former coca-growers union leader won in December 2005 presidential elections.

But the same referendum also gave several of the rebellious governors renewed support in their provinces, where Morales' authority is tenuous at best.

Bolivia's chief prosecutor, Mario Uribe, said he would charge Gov. Leopoldo Fernandez and other top officials in Pando, the jungle province on the Brazilian border where at least 15 people were confirmed killed in political violence last week, with genocide for provoking "a bloody massacre."

Morales says thugs used machine guns against his supporters in an ambush last Thursday, prompting him to declare martial law in Pando. But Fernandez remains defiant, saying the deaths came not in an ambush but an armed clash, that Morales is persecuting him politically and that he will stay put in Pando's capital of Cobija. "I won't flee," he said.

Bolivia's interior minister, Alfredo Rada, said Monday night that 15 people were confirmed killed in Pando. A day earlier, he had put the death toll at 30. Rada said, however that 106 people remained missing from Thursday's violent clash.

"According to witnesses, many of the missing are hurt, have fled into the hills and their lives could be in danger," Rada said.

Many of the anti-Morales blockades were dismantled over the weekend as a goodwill gesture as both sides sought to establish ground rules for negotiations. And while Bolivia was generally quiet on Monday, more than a thousand government supporters marched on the U.S. Embassy in the capital of La Paz, burning an American flag and effigies of opposition governors.

On Sunday, the U.S. Embassy issued a statement encouraging American citizens to leave Bolivia "if the situation permits," and said it has authorized the departure of all non-emergency embassy personnel and of family members.

Morales has expelled Washington's ambassador, accusing him of encouraging the unrest. Venezuelan President Hugo Chavez expelled his country's U.S. ambassador last week in solidarity with Morales, and the U.S. responded in kind.

Arriving in Chile on Monday, Chavez said "a conspiracy directed by the U.S. empire" was at work in Bolivia. He compared it to the 1973 coup, supported by the CIA, that toppled Chile's President Salvador Allende.

On his way out of La Paz on Sunday, U.S. Ambassador Philip Goldberg called the allegations "false and unfounded" and denied that his meetings with opposition governors and Washington's distribution of aid to their states were an attempt to undermine Morales.

Bolivia's opposition didn't participate in the summit in Chile, and it wasn't immediately clear how rhetorical support for Morales in Santiago might help solve the political crisis. But Morales' vice president, Alvaro Garcia, met Sunday night with Tarija Gov. Mario Cossio, representing the opposition governors, to try to establish ground rules for talks.

Meanwhile, anti-Morales forces still occupied ransacked government offices, and backers of the president kept up highway blockades cutting off the opposition stronghold of Santa Cruz. And in Pando, the Bolivian army arrested 10 people allegedly involved in Thursday's killings, the government news agency ABI reported. State television displayed seized weapons including a machine gun.