A technical mission from the Organisation of American States (OAS) began on Thursday to audit the results of the disputed Bolivian presidential election that delivered Evo Morales a fourth term but sparked deadly riots.
Announcing the news alongside OAS mission chief Arturo Espinoza, Bolivia's foreign minister Diego Pary said the audit was expected "to last two weeks."
Morales narrowly claimed the 10-point gap needed to win the October 20 election outright, but only after a sudden and unexplained shift in the vote count in his favor.
The opposition, led by Carlos Mesa, quickly denounced the results as "fraud."
Riots broke out almost as soon as the election ended, with supporters of the two main rivals fighting street battles with their bare hands and makeshift weapons.
Opposition supporters have set up street barricades and many people have also gone on strike.
Demonstrators have also clashed with security forces.
Mesa said earlier this week that the Morales administration "is entirely responsible for the violent actions."
However Vice President Alvaro Garcia Linera blamed Mesa for the clashes, calling him "angry, a liar and deceitful."
The 30-member OAS team will scrutinise the election result following an agreement between the government and the US-based grouping of 35 nations.
The government invited Mesa to take part in the audit, but the 66-year-old politician refused.
"We don't accept the audit with these unilaterally agreed terms," said Mesa, who has called for the results given by the electoral court (TSE) to be annulled as a precondition to participate in a scrutiny.
The Catholic Church said on Thursday it hopes the audit will lead to "an agreement" between the government and opposition, and called on both sides to "collaborate to bring peace to the country."
Morales, 60, was looking set to head into an election run-off against Mesa until the TSE abruptly changed the ballot count, increasing the president's lead and helping him to the crucial 10-point gap.
The OAS expressed "surprise" and "concern" over the sudden change.
The European Union and United States are among the foreign powers calling for a run-off.
Morales has said the protests are part of a "coup d'etat" encouraged by Mesa, who vowed "either I go to jail or I go to the presidency."
Morales, Bolivia's first indigenous president, has been in power since 2006, making him Latin America's longest-serving leader. The victory would allow him to remain in power until 2025 with a fourth term.
Though Bolivia's constitution limits a president to two successive terms, and a 2016 referendum rejected a bid by Morales to remove term limits, the country's constitutional court authorized him to stand for a fourth mandate.
The court, like the election tribunal, is made up of members appointed by Morales's Movement for Socialism.