The politician son of the far-right favourite to become Brazil’s next president has been evicted from WhatsApp amid allegations that his father’s push for power has been turbocharged by an illegal fake news blitz on the Facebook-owned messaging app.

One of Brazil’s top newspapers on Thursday claimed Brazilian entrepreneurs were bankrolling a multimillion-dollar campaign designed to boost Jair Bolsonaro by inundating WhatsApp users with messages undermining his leftist rival Fernando Haddad.

Haddad called for Bolsonaro to be barred from the presidential race as a result of what he called a criminal “defamation campaign” of fake news and lies.

Polls suggest Bolsonaro – a pro-torture former army captain who enjoys an 18-point lead over Haddad – is on course for a landslide victory in the 28 October runoff vote.

The latest twist in an increasingly dramatic race for the presidency – during which Bolsonaro suffered a near-fatal campaign trail stabbing – came on Friday when his son, Flávio Bolsonaro, claimed he had been banished from WhatsApp.

Flávio Bolsonaro tweeted a screenshot of his smartphone showing a message in Portuguese that read: “Your telephone number … is banned from using WhatsApp. Please contact support for help.”

A perseguição não tem limites!

Meu WhatsApp, com milhares de grupos, foi banido DO NADA, sem nenhuma explicação!

Exijo uma resposta oficial da plataforma.#MarketeirosDoJair #FolhaFakeNews pic.twitter.com/7Qpy1wakp3 — Flavio Bolsonaro (@FlavioBolsonaro) October 19, 2018

“There are no limits to this persecution,” Bolsonaro, a newly elected senator and a key member of his father’s campaign, wrote.

“My WhatsApp, with thousands of groups, was banished OUT OF NOWHERE, without any kind of explanation! I demand an explanation from the platform.”

In a second tweet Bolsonaro confirmed his account had been blocked several days ago and had now been reactivated “but without a clear explanation for this censorship”.

A WhatsApp representative said it had “proactively banned hundreds of thousands of accounts during the Brazilian election period”.

“We’re also taking immediate legal action to stop companies from sending bulk messages on WhatsApp and have already banned accounts associated with those companies,” the representative added.

The Folha de São Paulo reported that WhatsApp had also blocked the accounts of four companies involved in what it called the illegal mass sending of election-related WhatsApp messages.

Jair Bolsonaro has rejected claims he was involved in the fake news campaign, calling such allegations fake news. “We don’t need fake news to fight Haddad. The truth is more than enough,” he said in a Facebook live broadcast on Thursday night.

One of the most outlandish lies being peddled involves the bogus claim that, as São Paulo’s mayor, Haddad equipped schools with so-called “mamadeiras eróticas” (erotic baby bottles) with penis-shaped teats in an supposed bid to fight homophobia.