Protesters mobbed the streets outside Brazil's presidential palace after President Dilma Rousseff appointed embattled former president Luiz Inacio Lula da Silva as her chief of staff amid a corruption probe. (Reuters)

Police broke up fights between opposing groups of demonstrators outside Brazil’s National Congress building and protests flared in other cities Thursday as the country descended into political chaos amid a standoff between the judiciary and the government.

The cause: a political corruption scandal threatening to engulf two of Brazil’s most powerful leaders. “This is the worst crisis Brazil has had in recent decades,” said David Fleischer, emeritus professor of political science at the University of Brasilia.

The anti-government protests were provoked by President Dilma Rousseff’s decision to give her predecessor Luiz Inácio Lula da Silva a top cabinet post — a move that sent tens of thousands of Brazilians onto streets nationwide Wednesday night.

Lula, a former union leader and two-time president, is being investigated for his alleged role in a multibillion-dollar scheme in which kickbacks and bribes were paid on fat contracts at the state-run oil company, Petrobras. His appointment as Rousseff’s chief of staff was widely seen here as an attempt to protect him legally, because cabinet ministers and lawmakers can be investigated only by Brazil’s Supreme Court.

Brazil's President Dilma Rousseff and former president Luiz Ignacio Lula da Silva, attend a Workers Party's campaign rally in Sao Paulo in 2014. (Andre Penner/AP)

As Lula was sworn in Thursday morning, there were protests in at least 15 states, the G1 news site reported. Then a federal judge, Itagiba Catta Preta, suspended his nomination. Many cheered that decision even though a higher court could soon overturn it. Intensifying the pressure, federal judges in Sao Paulo, Curitiba and other cities demonstrated in support of the probe threatening Rousseff and Lula.

The events marked the latest dramatic twists in a corruption investigation known as Operation Car Wash that has relentlessly extended its reach up Brazil’s political ladder.

On Sunday, hundreds of thousands of Brazilians called for Rousseff’s impeachment and an end to corruption in demonstrations across the country. On Tuesday, the Supreme Court accepted testimony from the former leader of Rousseff’s Workers’ Party in the Senate in which he alleged that dozens of politicians were involved in this and other corruption schemes and that Rousseff and Lula had attempted to interfere in investigations. The allegations also cited Aécio Neves, a leading opposition senator who ran against Rousseff in the 2014 election. Neves has denied the claims.

Lula is a target of inquiry for Sergio Moro, a federal judge on a lower court whom anti-government protesters have embraced for his crusading role in the Petrobras investigation. On Wednesday evening, Moro escalated tensions when he authorized release of a recording of a telephone call that day between Rousseff and Lula.

In the short call, Rousseff told Lula that she was sending the papers confirming his ministerial role “in case of need.” Prosecutors said that this and other wire­tapped conversations whose transcripts were also released represented attempts to interfere in investigations.

A statement from Rousseff’s press secretariat said the terms of office were delivered to Lula to sign because it was not certain he would be able to attend the swearing-in ceremony planned for Thursday. At the ceremony, which Lula did attend, Rousseff brandished the document during an angry speech in which she attacked Moro and the wiretaps.

“There is no justice for citizens when constitutional guarantees of the president of the republic herself are violated,” she said. “Coups start like this.”

Brazilian President Dilma Rousseff says that former president Luiz Inacio Lula da Silva will help steer the ailing economy back on track as the newly appointed chief of staff, while her administration battles accusations of corruption. (Reuters)

Rousseff said Lula was being appointed because of his political capabilities.

Legal experts questioned both Moro’s and Rousseff’s moves.

Ivar Hartmann, a law professor at the Getulio Vargas Foundation’s law school in Rio, said Moro had done a good job in Operation Car Wash but had acted unlawfully in releasing the wiretaps.

“This time he overstepped his bounds,” Hartmann said.

Hartmann also said that while Rousseff had many good reasons to appoint Lula, a skilled political negotiator, to her cabinet at a time when Brazil is sinking deeper into recession and her government is at odds with its main coalition allies, the call’s timing suggested that “the main reason to invite him now was to avoid the arrest.”

There were protests Wednesday night in at least 18 Brazilian states, according to the G1 news site. Various cities also saw episodes of protesters banging pots and blaring car horns.

“How wonderful,” tweeted João Woerdenbag Filho, a rock singer known as Lobão. “We know that the Workers’ Party will leave as the biggest villains in the history of Brazil.”

But as news of the wiretaps spread, others argued that media coverage was biased against the government and that Operation Car Wash was no longer a neutral inquiry.

Nana Queiroz, a journalist and feminist activist in Brasilia, wrote on Facebook that Moro had made it “clear that he has a side and a bias in this story instead of being an impartial judge, as his job demands.”

Others voiced disillusionment with both sides. In Sao Paulo, Alessandra Boin, 42, shared a comment on Facebook: “It’s difficult. On one side, a government you can’t defend, on the other, an opposition you can’t support.”

Many of the phone calls released revealed Lula railing against the investigation in a blur of four-letter words. But in one conversation from March 4, he appeared to ask Jacques Wagner, the outgoing chief of staff and a former defense minister, to suggest to Rousseff that she attempt to influence a Supreme Court judge.

“Democracy is a free society that demands that those governed know what those who govern them do, even when they seek to act protected by the shadows,” Moro wrote in his decision to release the wiretaps.

As the uncertainty mounted, further protests against what the Brazilian left argues is an attempted institutional coup were planned for Friday in a number of cities.

Read more:

An oil scandal is shaking Brazil’s democracy to its core

Today's coverage from Post correspondents around the world