Brazilian police began questioning 23 people arrested as part of a wide-ranging probe into allegations of a multibillion-dollar kickback scheme at state-owned oil giant Petrobras.
A plane with 16 suspects, including former Petrobras director of engineering and services Renato Duque and nine executives from construction companies that signed fraudulent contracts with the oil firm, arrived at dawn in the southern city of Curitiba for questioning, according to Globo newspaper.
Four other suspects who turned themselves in Friday evening will also be questioned, while five remain at large.
In Sao Paulo's otherwise calm downtown area, police said some 2,500 people protested against corruption linked to the government of newly re-elected President Dilma Rousseff, a former Petrobras board chair.
On Friday, 27 people were arrests in raids across Brazil by 30 police teams that fanned out across the country to scoop up the suspects. Police said the network moved some $3.8 billion.
Authorities, under pressure to get to the bottom of the escalating crisis at Petrobras, also froze assets worth 720 million reais ($277 million) belonging to 36 suspects and three unnamed companies.
Former Petrobras director Paulo Roberto Costa has said the company allegedly paid millions of dollars in kickbacks to politicians and members of the ruling Workers Party between 2004 and 2012 to buy influence in what critics say was a collusion between Petrobras and politicians.
Costa, who is under house arrest, has been acting as whistleblower as part of a plea bargain with prosecutors. The allegations roiling Petrobras have been dubbed "Operation Car Wash."
On Saturday, Brazilian Justice Minister Jose Eduardo Cardozo accused opposition of using the episode to discredit Rousseff's October reelection.
The government will continue to demand "that we investigate everything... I say this to strongly discredit attempts to orchestrate, with this investigation, a third electoral round," he said during a press conference in Sao Paulo.
Just before the second round of voting in October, news magazine Veja quoted a suspect in the case as saying Rousseff and predecessor Luiz Inacio Lula da Silva knew about the kickbacks scheme, a claim both angrily denied.
Rousseff, who served as energy minister under Lula, threatened to sue Veja for publishing the allegations, which now are the subject of an investigation by the courts as well as Congress.
Petrobras said Thursday it was delaying the release of its third-quarter results because of ongoing corruption investigations involving the company.