Jeanine Añez claimed the post of Senate leader late in the day, a position next in line for the presidency, even though she lacked a quorum because of a boycott by Morales' Movement for Socialism party. Without being sworn in by anyone, she then appeared on a balcony of the old presidential palace wearing the presidential sash and holding a Bible in her hand.

"My commitment is to return democracy and tranquility to the country," she said. "They can never again steal our vote."

It was uncertain how much support Añez could count on from other power centers in her bid to replace Morales, who stepped down Sunday under pressure from Bolivia's military following weeks of violent protests fed by allegations of electoral fraud in the Oct. 20 presidential election.

Some Bolivians quickly took to the streets cheering and waving national flags in opposition strongholds like the cities of Santa Cruz and Cochabamba, but angry Morales' supporters tried to reach the Congress building in La Paz screaming, "She must quit!" Police and soldiers fired tear gas trying to disperse the crowd and detained some demonstrators.

Morales, who sought to transform Bolivia as its first indigenous president, had faced weeks of widespread outrage over his claim to have won the election outright. He stepped down soon after an Organization of American States audit reported widespread irregularities in the vote count.

He arrived in Mexico on Tuesday under a grant of asylum. But his resignation still needed to be approved by both houses of Congress, and lawmakers could not assemble the numbers needed for formal sessions.

Añez, a 52-year-old lawmaker, women's rights activist and television presenter, forged ahead anyway, arguing that Bolivia could not wait and be left in a power vacuum. After Morales quit, resignations by allies left vacancies in the only posts listed by the constitution as presidential successors — the vice president, the head of the Senate and the leader of the lower house.

Añez was a second-tier opposition figure until Morales resigned Sunday after nearly 14 years in power, the longest presidential reign ever in Bolivia.

From the start, she tried to set differences with the socialist leader. She greeted supporters at an old palace instead of the nearby modern 26-story presidential palace with a heliport that was built by Morales and that his foes had criticized as one of his excesses. She also carried a Bible, which had been banned by Morales from the presidential palace.

Morales said on Twitter from Mexico that Añez's "self-proclamation" was an affront to constitutional government. "Bolivia is suffering an assault on the power of the people," he wrote.

Even before Añez acted, thousands of his supporters were in the streets of the capital in peaceful demonstrations clamoring for his return.  Military fighter jets flew repeatedly over La Paz in a show of force that infuriated Morales loyalists who were blocked by police and soldiers from marching to the main square.

"We're not afraid!" shouted demonstrators, who believe Morales' departure was a coup d'etat and an act of discrimination against Bolivia's indigenous communities.

"Evo was like a father to me. We had a voice, we had rights," said Maria Apasa, who like Morales is a member of the Aymara indigenous group.

Morales' detractors accused him of becoming increasingly authoritarian and rigging the election.

Morales was met at Mexico City's airport by Foreign Secretary Marcelo Ebrard after a flight from Bolivia on a Mexican government plane and repeated his allegations he had been forced to resign by a coup.

"The president of Mexico saved my life," Morales said, thanking President Andrés Manuel López Obrador for granting him asylum. He vowed to "continue the struggle."

Ebrard said Mexican diplomats had to scramble to arrange a flight path for the plane because some nations initially closed airspace to it. The plane stopped in Paraguay to refuel.

Morales' departure was a dramatic fall for the one-time llama shepherd from the Bolivian highlands and former coca growers' union leader who as president helped lift millions out poverty, increased social rights and presided over nearly 14 years of stability and high economic growth in South America's poorest country.

In the end, his downfall was prompted by his insistence on holding onto power. He ran for a fourth term after refusing to accept the results of a referendum that upheld term limits for the president — restrictions thrown out by a top court that critics contend was stacked in his favor.

Gen. Williams Kaliman, chief of the armed forces, announced a joint police-military operation in a television address Monday seeking to calm street fighting. He said the hope was to "avoid bloodshed and mourning of the Bolivian family," and he urged Bolivians to help restore peace.

Ronald Arias said he had left his home in El Alto and walked for three hours to his job in downtown La Paz because the cable car connecting the cities was suspended for security reasons and barricades blocked access to public transportation.

Arias, a native Aymara, said that thanks to Morales, his parents in the countryside gained access for the first time to running water and gas for cooking.

"I was so saddened by his resignation," he said. "A lot of people in El Alto shed tears for the president."