Brasilia, November 23 (RHC)-- Former Brazilian President Luiz Inacio Lula da Silva has pledged to rally against incumbent Jair Bolsonaro's far-right government and the authorities he accuses of unjustly imprisoning him, saying he would "make their lives hell."

Addressing a conference of the leftist Workers' Party (PT) in Sao Paulo on Friday, Lula said he was "more willing to fight for this country than in any other moment" following his release from prison two weeks ago.

"Today I feel much stronger than the day I surrendered to the federal police," the 74 year old, who spent 19 months behind bars due to a corruption conviction, told supporters.  "You will see me travelling around this country, not only making their lives hell but also defending the Brazilian people who don't deserve to experience what they experiencing," added the former union leader.

Lula was freed from prison on November 8th following a Supreme Court ruling which overturned the court's opinion three years ago that convicted criminals face mandatory imprisonment if they lose their first appeal.

Following his release, speculation has mounted over whether Lula -- a PT founding member who governed Brazil from 2003 to 2010 -- could be the PT's candidate in the country's 2022 presidential election, even though he is currently barred from running for office due to the corruption conviction that led to his jailing.

Under Brazil's "Clean Slate" legislation, people with serious criminal convictions are prevented from standing for office within eight years of them being found guilty.

In 2018, Lula was handed a nearly nine-year sentence after being found guilty of receiving bribes from construction companies in return for public contracts as part of a sweeping probe into corruption known as Lava Jato, or Car Wash.  He is also facing several other corruption charges.

Lula has always rebutted the allegations, insisting the case against him was politically motivated and accusing prosecutors and Sergio Moro -- then a judge and now justice minister in Bolsonaro's government -- of manipulations.

He is appealing against his conviction related to the alleged purchase of a beachfront apartment as well as the judgement in a case involving ownership of a farmhouse in Atibaia, outside Sao Paulo.

If he loses his appeals in either conviction, however, he could be locked up again.  The cases may continue winding through the courts for years.

Born in rural northeastern Brazil in 1945, the charismatic Lula left office with personal approval ratings approaching 90 percent having presided over a period of prosperity and reduced poverty.

Despite the corruption cases brought against him and his imprisonment at the time, Lula also topped opinion polls in the run-up to Brazil's 2018 highly-polarised presidential election -- eventually won by Bolsonaro -- before being forced to withdraw his candidacy for the country's top seat a month before the vote.

Bolsonaro's popularity appears to be on the wane, with his approval rating collapsing to just over 30 percent in recent months, down from 49 percent at the beginning of this year, according to polling by the Brazilian Institute of Public Opinion and Statistics.

The 64-year-old former army captain said Brazil should not "give space to compromise with a convict" following Lula's release and has urged supporters to rally around his government's agenda, which has included a severe tightening of public spending.

Lula, for his part, has accused Bolsonaro of wanting to "destroy all of the democratic and social conquests" the country had made since transitioning to democracy in 1985 after two decades of military rule while also calling for a tamping down of political polarisation.

"I regret that Brazil is becoming a country where spreading hate is becoming part of people's daily lives," he told The Guardian newspaper in an interview published on Friday.