Brazilian President Luiz Inácio Lula da Silva's campaign has requested the disqualification of right-wing challenger Flávio Bolsonaro in the lead up to the final round of the presidential election on Sunday over alleged interference by social media company Meta.

In a petition filed to the country's top electoral court on Wednesday, the leftist incumbent president accused Meta, the tech giant behind Whatsapp, Instagram and Facebook, of limiting its content to boost Bolsonaro's campaign.

In response, Bolsonaro filed a petition seeking to disqualify Lula over what he said was the mass dissemination of government posts on WhatsApp. The company has denied the campaigns have been treated unequally.

It comes after UN experts said on Wednesday that they were concerned about reports of discrepancies in the ability of each campaign to reach voters on Meta's platforms.

A report led by the UN's special rapporteur on freedom of expression said Meta must ensure a level playing field online during the election.

It cited incidents including "temporary interruptions of one candidate's campaign account; differences in audience engagement, user feeds, view counts and reach; restrictions on that campaign's Instagram posts".

"Information, including from Meta employees, suggests that accounts linked to one side of the presidential race were disproportionately curtailed," it read.

Meta has denied taking action to favour one side of the election and has said it would comply with an order from a Brazilian court to treat Bolsonaro and Lula equally.

Lula's campaign had previously filed a complaint alleging that accounts and content related to Bolsonaro were boosted. Users also reported that Meta's artificial intelligence tools were not generating images related to Lula. Brazilians will head to the polls on Sunday as Lula seeks a fourth term in office.

Bolsonaro beat Lula in the first round of voting on 4 October by a narrow margin, but fell short of the 50% of valid votes needed to win outright.

On Wednesday, Lula's campaign filed a petition to Brazil's Superior Electoral Court (TSE) for Bolsonaro and Alfredo Gaspar, his candidate for vice-president, to be investigated over "abuse of economic power and improper use of social network".

The petition also seeks to make Bolsonaro ineligible to stand for election for eight years following the 2026 election.

Meanwhile, Flávio Bolsonaro, the son of convicted former president Jair Bolsonaro, accused his rival of "abuse of political and economic power".

He claims the government has used personal data taken from official databases to send mass messages on Whatsapp to promote social programmes.

Opinion polls suggest Sunday's run-off will be extremely close, with little separating the two as Brazil's 159 million registered voters prepare to go to the ballot boxes.