Evo Morales defied term limits to run for president again last month, then declared victory in an election widely seen as rigged.
Bolivia’s military chief on Sunday called on President Evo Morales to resign, dealing what was likely a fatal blow to his efforts to cling to power in the face of widespread unrest over last month’s fraud-marred presidential elections.
The commander of Bolivia’s armed forces, Gen. Williams Kaliman, said the military chiefs believed Mr. Morales should step down to restore “peace and stability and for the good of our Bolivia.”
Earlier in the day, facing mounting opposition from political rivals, mutinous police groups and outraged protesters, Mr. Morales called for a new election. It was an extraordinary concession in the face of mounting evidence of electoral fraud — but it appeared to accomplish little.
Unappeased, demonstrators and opposition leaders renewed demands that Mr. Morales step down.
“Mr. Evo has ruptured the constitutional order — he needs to leave,” said Luis Fernando Camacho, one of the main protest leaders.
Several leading figures in his party resigned, and the military launched operations that appeared intended to protect protesters from violent bands of Morales supporters who have killed several protesters and wounded scores.
Mr. Morales, the first Indigenous president in a country where two-thirds of the population is Indigenous, has been in power longer than any other current head of state in Latin America. Once widely popular, he has become increasingly authoritarian.
The unrest has turned Bolivia into the latest flash point in a series of upheavals that have shaken Latin America over the last month.
In recent days, evidence has mounted that Mr. Morales’ party rigged last month’s presidential election. But even before the vote was cast, the opposition was accusing the president of acting illegally by changing the Constitution so he could run for an unprecedented fourth term.
The Organization of American States, which monitored the Oct. 20 election, issued a preliminary report on Sunday that outlined irregularities and said the vote should be annulled.
Carlos Mesa, the former president who came in second in the disputed election, has said that the country’s political parties should come together and organize a new vote. On Sunday, he lashed out at the president and the vice president on Sunday for “this fraud, and the social unrest that has led to several deaths and hundreds of people wounded.”
Michael Kozak, the top diplomat at the State Department overseeing Latin America policy on Sunday endorsed the call for a new election. “All those implicated in the flawed process should step down,” he wrote on Twitter, without addressing the question of whether Mr. Morales should be eligible to run again.
Demonstrations calling for the president to step down and allow for new elections appeared to reach critical mass on Saturday, when groups of police officers across the country broke ranks with the government and joined anti-government protests.
In his televised address Sunday, Mr. Morales called for peace and said he would replace the Electoral Tribunal and hold a new vote, though he did not specify a date. The opposition had accused the tribunal favoring Mr. Morales and taking part in election fraud.
Mr. Morales said the new election would be a “vote that will allow the Bolivian people to democratically elect their new leaders, incorporating new political actors.”
Martha Yujra, a member of a workers union in El Alto, the municipality adjacent to La Paz that had been a traditional Morales stronghold, said Sunday that protesters would remain in the streets until Mr. Morales steps down.
“He has to resign,” she said. “He can’t call for a new election.”
Mr. Morales’ speech came hours after the Organization of American States released its preliminary report outlining widespread irregularities.
The O.A.S. report bolsters the widely held view among Bolivians critical of Mr. Morales that the president and his allies, facing the toughest electoral battle since he came to power in 2006, engaged in a concerted effort to rig the vote.
Election officials said Mr. Morales received slightly more votes than he needed on Oct. 20 to avoid a runoff.
But the legitimacy of that victory was called into question almost immediately because that finding contradicted early results, which showed he had not won by more than 10 percentage points, the threshold needed for a runoff.
By Saturday night, the unrest had spread to Mr. Morales’s stronghold of El Alto, where government supporters and protesters clashed on the streets, according to local news reports.
In the countryside, where Mr. Morales remains popular with poor farmers, government supporters blocked and attacked with stones and firearms several caravans of protesters heading to demonstrations in La Paz.
Calla Hummel, a political scientist at the University of Miami who has done extensive field research in Bolivia, said Mr. Morales was unlikely to weather this crisis.
“His actions have undermined his reputation as a democratic leader,” Ms. Hummel said on Sunday. “The opposition is now more unified and mobilized now than the disparate groups were during the election.”
Ms. Hummel said the military’s hands-off approach — at least until now — was unsurprising, because the generals fear being dragged into the kind of street clashes that roiled the country in 2003. In the aftermath of those confrontations, several soldiers were prosecuted for killing demonstrators.
“The military does not want to be handed this situation,” Ms. Hummel said. “Anything is possible in Bolivia right now, but a military coup is very, very unlikely.”