RIO DE JANEIRO (Reuters) - Earlier this week, Brazil’s far-right presidential candidate Jair Bolsonaro said the presidency was “within reach.” Just a day later though, Bolsonaro had to deny he had indulged in the same skullduggery he has often accused his leftist opponents of masterminding.

Presidential candidate Jair Bolsonaro attends a news conference in Rio de Janeiro, Brazil October 11, 2018. REUTERS/Ricardo Moraes

Despite increasing his lead in an opinion poll over leftist Workers Party (PT) candidate Fernando Haddad on Thursday, Bolsonaro was forced to deny accusations by Haddad that he had asked business leaders at a dinner in Sao Paulo for funds to pay for bulk propaganda messaging on WhatsApp, which would be a campaign finance violation.

The PT filed an official complaint with the election tribunal asking it to investigate, injecting a dose of uncertainty into an election race that has looked increasingly one-sided in recent weeks.

Bolsonaro has ridden a wave of anger over years of graft, and rising violence, accusing the PT, which ran Brazil for 13 of the last 15 years, of destroying Brazil and killing its economy.

The anti-establishment candidate, who has represented Rio de Janeiro state as a federal congressman for nearly three decades, has won supporters thanks to a career untainted by corruption accusations.

Nonetheless, his top economic adviser is being investigated by federal prosecutors over accusations of fraud tied to the pension funds of state-run companies, underlining the scale of the rot in Brazil’s political landscape.

The Folha de S.Paulo newspaper reported on Thursday that well-heeled Bolsonaro supporters had paid for messaging by third-party agencies, with each spending up to 12 million reais ($3.26 million) to spread tens of thousands of attack ads.

The report energized Haddad, who said his party has witnesses saying Bolsonaro asked business leaders for cash to pay for the bulk messaging, which he described as undeclared campaign contributions. A representative for WhatsApp, which is owned by Facebook Inc FB.O, said the report was being taken seriously.

Campaign propaganda has flooded social media in Brazil ahead of an Oct. 28 run-off vote in the presidential election. The issue of fake news and abuse of social media has been a growing concern in elections across the world, and tech companies have come under growing pressure to limit misinformation.

It was unclear what effect, if any, the accusations would have on opinion polls. A Datafolha survey, taken before the campaign finance allegation was made public, showed Bolsonaro had 59 percent of voter support, compared to 41 percent for Haddad. Bolsonaro had 58 percent versus 42 percent for Haddad last week.