The Intercept website co-founded by Glenn Greenwald published a series of explosive articles Sunday based on material provided by an anonymous source that it said show "serious wrongdoing, unethical behavior, and systematic deceit" in the sprawling Car Wash investigation that has claimed scores of political and business scalps.

While claims that Justice Minister Sergio Moro, the anticorruption judge who handed Lula his first conviction in 2017, improperly collaborated with prosecutors were a "setback" for the probe, they were unlikely to result in overturning convictions or Moro's resignation.

"In the public imagination it is not at all shocking or something that undermines the legitimacy of the whole effort," Christopher Garman of Eurasia Group told AFP.

While the revelations would fuel the "free Lula" movement and "give fodder" for legal challenges to ongoing Car Wash investigations, they would at best fast-track the popular ex-politician's release into home detention, he said.

"They do not change, in substance, the reason for the convictions even though they reveal inappropriate comments (by investigators)," said ex-president Fernando Cardoso in remarks published by the UOL website.

There could be "some fallout, probably, but no big deal," David Fleischer, a political science professor at the University of Brasilia, told AFP.

Debate over the leak erupted on Twitter, with #EuApoioLavaJato, (#ISupportCarWash) and #EuApoioTheInterceptBR among the top trending topics in Brazil, exposing the country's deep political divisions.

"We shouldn't discard the real possibility the conversations were forged, creating #fakenews," tweeted Marcelo Bretas, a judge in the Car Wash probe in Rio de Janeiro.

Greenwald fired back: "Implying that the material is 'fake' is a dirty tactic, especially for a judge. Your friends in court and LJ (Lava Jato) who behaved in an unethical way could only reveal the content. But they do not even claim that the documents are 'fake' because they know they are real. You know that too."

Bolsonaro, normally very outspoken on Twitter, has been unusually quiet.

Among the explosive claims, The Intercept said Car Wash prosecutors had expressed "serious doubts whether there was sufficient evidence to establish Lula's guilt."

The leaked material also shows "Car Wash prosecutors spoke openly of their desire to prevent the PT from winning the (2018) election and took steps to carry out that agenda," The Intercept said.

In response to the reports, Moro defended his actions as judge in the ongoing probe and cast doubt on the authenticity of the messages hacked from prosecutors' cell phones.

Lula, who led Brazil through a historic boom from 2003 to 2010, has denied all the corruption charges against him, arguing they were politically motivated to prevent him from competing in the elections.

He is serving a reduced jail term of eight years and 10 months after being convicted of accepting a seaside apartment as a bribe for helping the OAS construction company get lucrative deals with Petrobras.

While behind bars, Lula's Workers' Party (PT) registered him as their presidential candidate in August 2018 -- two months before the election he was widely expected to win.

An electoral court barred him two weeks later and far-right President Jair Bolsonaro went on to win the ballot.