Socialist Pedro Castillo is closing in on victory in Peru's presidential election, prompting allegations of fraud by conservative rival Keiko Fujimori and the US.
Castillo on Thursday held some 50.2% of the vote and a 0.36 percentage point lead with 99.4% of ballots tallied.
The school teacher and political novice has rattled the copper-rich Andean nation's traditionally political and business elite as he has won widespread grassroots backing for pledges to rewrite the constitution and redistribute mining wealth.
"The people have awakened," Castillo told supporters from a balcony in Lima late on Thursday, calling on citizens to recover the country for all Peruvians after a divisive election race.
Fujimori has not conceded defeat, and is seeking to annul some 500,000 votes which she says are suspicious.
Independent electoral observers, however, say the vote was carried out cleanly, while Castillo's Peru Libre party says there is no evidence of suspicious activity.
The ethics tribunal of the National Jury of Elections (JNE), the body charged with overseeing the legality of the electoral process, said on Thursday that throwing doubt on the results without evidence was "irresponsible."
Washington, nevertheless, said that electoral authorities should be allowed to look into any fraud allegations.
"We look forward to working with the duly elected candidate," a US State Department spokesperson said.
Despite being the world no.2 copper producer, Peru posted its worst economic plunge in three decades last year. The country has been hit by the world's deadliest COVID-19 outbreak by deaths per capita.
Last year, it saw three presidents in a week amid political scandals and protests.
Despite the US casting aspersions, many were already celebrating Castillo's victory in Latin America.
Argentina's President Alfredo Fernandez was the first world leader to congratulate Castillo, saying on Twitter he had contacted the "President-elect" and expressed wishes to join forces for the benefit of Latin America.
In Brazil, former president Luiz Inacio Lula da Silva, who is widely expected to challenge far-right President Jair Bolsonaro in next year's election, said Castillo had struck a blow against conservatism in the region.
"The result of the Peruvian polls is symbolic and represents another advance in the popular struggle in our dear Latin America," he said.
Bolivia's former President Evo Morales also congratulated Castillo on his "victory," calling him a "soul brother and companion in struggle."
Castillo's thin lead over Fujimori is more sizable than the 0.24% margin by which Fujimori lost to Pedro Pablo Kuczynski in the 2016 presidential election.
"Then, Fujimori did not demand a recount, but given the political and legal stakes for her, she may do this time round," said Eileen Gavin, principal analyst of Global Markets and the Americas for risk consultancy Verisk Maplecroft.
Fujimori is plagued by accusations she accepted illegal campaign contributions when she first ran for the presidency in 2011. She spent over a year in jail pending a trial.
On Thursday, prosecutor Jose Domingo Perez requested that Fujimori's bail be revoked and she be returned to custody pending the trial, arguing that she had been in contact with a witness.
"Prosecutors are entitled to seek her jailing, but it will be interpreted by people as an attempt to meddle with the electoral process," said Ernesto de la Jara, a Peruvian human rights lawyer.