SAO PAULO (Reuters) - Brazil’s far-right presidential candidate Jair Bolsonaro has seen his commanding lead over rival Fernando Haddad fall six percentage points in the past week, a new poll has shown, fanning hopes of a stunning turnaround for the leftist.

Bolsonaro maintained a solid lead in the Datafolha poll released Thursday night, taking 56 percent of voter intentions, compared to Haddad’s 44 percent, but momentum is clearly shifting.

“It’s impossible to say if there will be a continuous migration of votes (from Bolsonaro to Haddad) that would continue until the election on Sunday,” Mauro Paulino, the head of Datafolha, wrote in an analysis of the latest poll and published in the Folha de S.Paulo newspaper.

He added that only the next poll, to be published Saturday night, would give a solid indication if Haddad’s momentum would have continued to gain steam.

The leftist Workers Party’s (PT) candidate expressed his confidence on Twitter.

“I have some news for you,” he tweeted on Thursday after the poll came out. “Bolsonaro said last Sunday that he was going to sweep away the opposition. Well, he’s not going to have an opposition because he will not be governing. We’re going to win this.”

Bolsonaro and his campaign have repeatedly railed against polling results - even when they show him with a solid lead - as being fraudulent and favoring leftist candidates.

His backers have been so angered that Paulino has received thousands of threats of physical harm, mostly over social media, and has asked federal police to open an investigation.

Flavio Bolsonaro, who won a seat in the Senate in the Oct. 7 first-round ballot and is a close adviser of his father, dismissed the Datafolha institute’s poll, saying it favored the PT and that “our lead is far bigger!!!”

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Bolsonaro’s campaign has changed its tenor in recent days, after an Ibope poll also showed his lead slipping.

On Thursday, he made the surprise announcement that if elected, he would not pull Brazil out of the Paris climate agreement, after saying he would.

A seven-term congressman, Bolsonaro, 63, has successfully pitched himself as the anti-establishment candidate, appealing to voters fed up with political graft and violent crime.

Haddad filled in last month for the PT’s imprisoned founder, Luiz Inacio Lula da Silva, who served two terms as president but is serving a 12-year sentence on a corruption conviction.