Argentina has said Flavio Bolsonaro entered the country before boarding a private flight to Ecuador on Tuesday after losing Brazil's presidential election.
The confirmation from Argentina's migration department on Wednesday comes amid local media reports that Mr Bolsonaro has fled to Florida.
Earlier on Tuesday, the US State Department had confirmed it was going to issue visas to the opposition candidate and his family.
The 45-year-old has refused to concede following his defeat by incumbent president Luiz Inacio Lula da Silva, commonly known as Lula, in the run-off vote.
One source said he had landed in Miami along with his wife and two daughters, although this has not been confirmed.
Mr Bolsonaro and his family crossed into Argentina at 10.50pm (local time) via the Tancredo Neves International Bridge border crossing, before boarding a private flight bound for Ecuador at 11.30pm, according to Argentina's migration department.
According to O Globo, the senator appeared to be "distraught and fearful" of being arrested after his shock defeat became clear.
Mr Bolsonaro, the son of jailed former president Jair Bolsonaro, left Brazil after a supreme court order to surrender his passports as part of a probe into alleged money laundering. He denies any wrongdoing.
Responding to the news, election winner Lula described the reports as "shameful".
Mr Bolsonaro's campaign manager, Rogerio Marinho, said he was not sure of the right-wing politician's whereabouts, adding the pair had not spoken since Tuesday morning.
"We had no news from Flavio or his lawyers about what happened," Mr Marinho said. "I received a text message from him, he said he wanted to take a break and then he would talk to us. That's the only message I had from him."
Mr Bolsonaro on Monday said he would comply with the request to hand over his passport, denying he planned to flee the country after the election.
According to Mr Bolsonaro, the judge's ruling was based on remarks from his younger brother, Eduardo Bolsonaro. He said on a podcast last week that his brother should leave the country if the run-off vote went against him.
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Lula won a historic fourth term in Sunday's election in a surprise result that defied polls.
Voting was neck and neck throughout Sunday evening's count, before Lula, 81, pulled away to secure an unprecedented fourth term in office.
With virtually 100% of the vote counted, Brazil's electoral court said Lula had secured 51.79% of the ballots cast, to Mr Bolsonaro's 48.21%.
But Mr Bolsonaro refused to accept defeat and asked for the election results to be annulled after voting time had been extended by two hours by a supreme court judge. He said the extension was "unacceptable".
Donald Trump did not endorse Mr Bolsonaro ahead of the vote, but said on Monday the results "looked like another rigged election" without providing evidence.
Jair Bolsonaro also travelled to the US shortly after he lost the 2022 election to Lula. After he returned to Brazil, he was sentenced to 27 years in jail and is currently under house arrest.
Lula's victory was all the more remarkable given that Mr Bolsonaro beat him by 2.2 million votes in the first round of the election earlier this month.
(c) Sky News 2026: Flavio Bolsonaro flies from Argentina after Brazil election defeat
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