LA PAZ, Bolivia -- Renewed clashes rocked Bolivia's capital on Wednesday as the country's newly declared interim president, a second-tier lawmaker thrust into the post because of a power vacuum, faced challenges to her leadership claim from supporters of ousted Evo Morales.

A day after Jeanine Anez claimed the presidency, violent clashes broke out between rock-throwing Morales' supporters and police in riot gear, who fired volleys of tear gas to disperse the large crowd of protesters.

Some demonstrators tore off corrugated sheets of metal and wooden planks from construction sites to use as weapons. Many had flooded the streets of the capital and its sister city of El Alto, a Morales stronghold, earlier in the day in a peaceful protest waving the multicolored indigenous flag. But some still chanted: “Now, civil war!”

“We don't want any dictators. This lady has stepped on us - that's why we're so mad,” said Paulina Luchampe. “We're going to fight with our brothers and sister until Evo Morales is back. We ask for his return. He needs to put the house in order.”

Anez faces the challenge of winning recognition, stabilizing the nation and quickly organizing national elections at a time of bloody political disputes that have pushed Morales, the nation's first indigenous leader, to fly into self-exile in Mexico after 14 years in power.

According to the constitution, an interim president has 90 days to organize an election, and the disputed accession of Anez, who until Tuesday was second-vice-president of the Senate, was an example of the long list of obstacles she faces. Morales' backers, who hold a two-thirds majority in Congress, boycotted the session she called to formalize her claim to the presidency, preventing a quorum.

Still, she took power anyway, saying the constitution did not specifically require congressional approval. “My commitment is to return democracy and tranquility to the country,” she said. “They can never again steal our vote.”

Bolivia's top constitutional court issued a statement late Tuesday laying out the legal justification for Anez taking the presidency - without mentioning her by name.

But other legal experts challenged the legal technicalities that led to her claim, saying at least some of the steps required Congress to meet.

And the lingering questions could affect her ability to govern.

Eduardo Gamarra, a Bolivian political scientist at Florida International University, said the constitution clearly states that Anez didn't need a congressional vote to assume the presidency. Even so, “the next two months are going to be extraordinarily difficult for President Anez,” he said.

“It doesn't seem likely” that Morales' party “will accept her as president,” said Jennifer Cyr, an associate professor of political science and Latin American studies at the University of Arizona. “So the question of what happens next remains - still quite unclear and extremely worrying.”

She will need to form a new electoral court, find non-partisan staff for the electoral tribunal and get Congress, which is controlled by Morales' Movement for Socialism Party, to vote on a new election.

Morales resigned Sunday following weeks of violent protests fed by allegations of electoral fraud in the Oct. 20 election, which he claimed to have won. An Organization of American States audit reported widespread irregularities in the vote count and called for a new election.

But his decision came only after Gen. Williams Kaliman, the armed forces commander, urged him to step down “for the good of Bolivia” - a move that Morales and his backers have branded a coup d'etat.

Anez swore in new commanders-in-chief in all branches of the military on Wednesday, replacing Kaliman, who had been a Morales loyalist, with Gen. Carlos Orellana. The move was seen as an effort to build an alliance with the military, although it was uncertain how much support she could count on from other Bolivian power centres.

Still, she received a boost of international support on Wednesday.

Michael G. Kozak of the U.S. State Department's Bureau of Western Hemisphere Affairs welcomed her as “interim constitutional president,” saying on Twitter: “We look forward to working with her & Bolivia's other civilian authorities as they arrange free & fair elections as soon as possible, in accordance w/ Bolivia's constitution.”

Brazil, which is one of Bolivia's top trading partners, also congratulated her on her “constitutional” assumption of the presidency and her determination to work for peace and hold elections soon.

The 60-year-old Morales, who arrived in Mexico on Tuesday under a grant of asylum, has vowed to remain active in politics. He decried Anez's “self-proclamation” as an affront to constitutional government. “Bolivia is suffering an assault on the power of the people,” he said in a Twitter post Tuesday night.

But at a news conference in Mexico City on Wednesday, he took a more conciliatory tone, urging a national dialogue with oversight by “friendly” countries and international organizations. He also called on police and the military to abstain from violence. “Don't get stained with the blood of the people,” he said.

From the start, Anez has tried to set herself apart from Morales. Wearing the presidential sash of office, she greeted supporters at an old presidential palace Tuesday night instead of the modern 26-story presidential office 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 palaceafter he reformed the constitution and recognized the Andean earth deity Pachamama instead of the Roman Catholic Church.

A one-time llama shepherd from the Bolivian highlands and former coca growers' union leader, Morales helped lift millions out poverty as president, increasing social rights and presiding over stability and high economic growth in South America's poorest country.

But even many supporters eventually grew weary of his long tenure in power - as well as his insistence in running for a fourth term despite a public referendum that upheld term limits, restrictions thrown out by a top court that critics contend was stacked in his favour.

Associated Press writers Natacha Pisarenko in La Paz, and Christopher Torchia in Mexico City contributed to this report.