SAO PAULO - Brazilian police have arrested the presidents of two of the country's largest construction companies for their alleged involvement in the massive corruption scheme at the state-run oil giant Petrobras.

Marcelo Odebrecht, head of Odebrecht SA, and Otavio Marques Azevedo, head of Andrade Gutierrez, were taken into custody in Friday morning raids.

Inspector Igor Romrio de Paulo of the federal police said at a news conference that Odebrecht and de Azevedo were taken into custody and face charges of cartel formation, money laundering and diversion of public funds.

Another eight executives from the two companies were also arrested. They will be taken to the southern city of Curitiba, where the investigation is based.

"We have money-laundering professionals in Brazil and we have no doubt that Odebrecht and Andrade Gutierrez headed the cartel scheme inside Petrobras," federal prosecutor Carlos Fernando dos Santos Lima said at the news conference. "I do not see how the companies can claim innocence given how much evidence we have."

He said the two men "had a sophisticated system" for making the alleged bribe payments, using foreign bank accounts in Switzerland, Monaco and Panama.

"We have material proof that they knew about the practice of overbilling contracts with Petrobras and they participated directly in the division of contracts within the cartel," investigator, Igor Romrio de Paula, said at a news conference Friday.

Prosecutors have said the scheme involved at least $800 million in bribes and other illegal funds. Some of that money was allegedly funneled back to the ruling Workers' Party and its allies' campaign coffers.

It also allegedly included the payment of bribes to Petrobras executives in return for inflated contracts.

Odebrecht said in an email statement that police searched the company's offices in So Paulo and Rio de Janeiro and that it considered the police operation unnecessary because Odebrecht was cooperating with the investigation.

In a similar statement, Andrade Gutierrez also said it was cooperating with authorities and denied any wrongdoing.

The two are the most senior corporate figures to be detained by police over investigations into allegations that Brazil's largest construction companies collaborated with former Petrobras executives and many politicians to extract bribes and kickbacks from the oil company.

The probe is looking into whether subcontractors may have colluded with top Petrobras executives to overbill the company and pay bribes.

The probe into Brazil's biggest corruption scandal is threatening to engulf the Workers' Party of President Dilma Rousseff and her predecessor Luiz Inacio Lula da Silva.

Odebrecht, 46, one of the country's richest men, has personal ties to former President Luiz Inacio Lula de Silva, which could bring the scandal closer to the political heart of the ruling Workers' Party.

President Dilma Rousseff, who was chairwoman of the Petrobras board during Lula's presidency, has denied knowledge of the corruption scandal dating to at least 2004 and urged a thorough investigation. Neither she nor Lula has been implicated.