The political party of Senator Flavio Bolsonaro has acknowledged the result of Brazil’s presidential run-off, despite the right-wing candidate pledging to annul the outcome.

On Monday, Valdemar Costa Neto, the leader of the right-wing Liberal Party, issued a statement saying his political group had accepted the outcome of the vote.

Still, he echoed Bolsonaro’s concerns about the circumstances surrounding the election.

“We recognise the presidential election results,” Costa Neto said. “But we believe the issues raised need to be properly clarified.”

On Sunday, Bolsonaro was defeated by left-wing incumbent President Luiz Inacio Lula da Silva by a margin of more than 4.4 million votes.

Bolsonaro has yet to formally concede. In a post-election speech, he called the election results “unacceptable”, citing a last-minute extension to voting hours.

“We will take legal action,” he told supporters. “I will request that these elections be annulled.”

An extension to Sunday’s vote had been sought by the campaigns of both candidates — but for different reasons.

Bolsonaro’s camp had pointed to inclement weather that impeded some voters from reaching polling stations. Parts of southern Brazil, considered a right-wing stronghold, had experienced heavy rains on Sunday.

Lula’s campaign, meanwhile, pushed for longer voting hours after it accused some cities of limiting public transportation on election day.

The left-wing leader’s allies framed those reductions in service as an attempt at election interference, aimed at preventing Lula’s working-class base from voting.

Media reports indicated that Pablo Souza, a transportation official in the city of Salvador, was arrested on Sunday over the matter.

In response to the petitions, Supreme Court Justice Cristiano Zanin agreed to extend voting by two hours.

Whereas polls across the country had been slated to close at 5pm Brasilia time (20:00 GMT), Zanin’s order allowed those that had not already closed to remain open until 7pm (22:00 GMT).

Following his loss, Bolsonaro cried foul, saying that the justice’s decision had disadvantaged his voters.

He pointed to Zanin’s relationship with Lula as support: Lula had appointed Zanin to the high court in 2023, and Zanin had formerly served as the left-wing politician’s personal lawyer.

“With a simple stroke of a pen, at the request of a former partner, [Zanin] changed the rules of the game mid-match,” Bolsonaro said in his address on Sunday night.

But experts signalled they were sceptical of Bolsonaro’s claims of malfeasance.

An analysis by Pedro Burgos, a professor at the Brazilian educational institute Insper, found that the extension resulted in 35,000 additional votes across the country, less than 0.03 percent of the total.

That amount was far short of Lula’s 4.4 million vote advantage. The incumbent won more than 64.25 million votes, compared with Bolsonaro’s 59.83 million.

Still, some right-wing allies rallied to Bolsonaro’s support. US President Donald Trump, who has clashed with Lula in the past, told reporters that the vote seemed “rigged”.

“Elections have to be indisputable and it looked very bad to me,” Trump said on Monday. “It looked like another rigged election, frankly.”

Still, Trump stopped short of suggesting that he would get involved on behalf of Bolsonaro, saying instead he “did not take sides” in the election.

Bolsonaro’s refusal to accept his loss has raised concerns about whether he will abide by the democratic process or follow in the footsteps of his father, Jair Bolsonaro, who served as Brazil’s president from 2019 to 2023.

After his defeat to Lula in the 2022 election, the ex-president refused to acknowledge the outcome.

Instead, he and his allies sought to overturn the results, including through a legal challenge, and prosecutors accused him of plotting a coup to prevent the legal transfer of power.

Jair Bolsonaro is currently serving a 27-year prison sentence on coup-related charges.

Separately, he was also barred from serving in public office for eight years, after a court found he had misused his public office to spread misinformation about the election.

Flavio Bolsonaro, along with his siblings, has sought to have his father released. The family has denounced the elder Bolsonaro’s trial as a case of political persecution.

Still, it is unclear whether Flavio Bolsonaro will continue with his legal challenge over Sunday’s election.

The Brazilian news outlet Folha de S Paulo reported on Monday that legal advisers and political allies have convinced Bolsonaro to abandon his quest to have his loss annulled, citing the large margin of Lula’s victory and its validation by the Supreme Court and election authorities.

Bolsonaro also announced on Monday that federal police asked him to hand over his passports amid speculation that he could leave the country following his loss.

He said that he would comply with the order and had no plans to leave.

“To withstand the chaos, I’m going to organise the opposition,” the right-wing politician said.