SÃ O PAULO—Brazil's giant state-run oil firm Petró leo Brasileiro SA, or Petrobras, said Friday it is tightening its supplier controls in the wake of a massive corruption scandal and seeking the reparation of about $2 billion that was diverted during a yearslong price-fixing scheme.

Petrobras said suppliers now will need to give detailed information on their finances and compliance mechanisms. It didn't explain how this would be different from its previous relationship with suppliers.

Petrobras also said it has undertaken internal initiatives to limit individual managers' power within the company, created two new committees and begun a process of hiring an independent, external ombudsman to help prevent future corruption.

The company will be limiting its individual executives' "ability to make a decision" and those decisions will be monitored by "committees and support groups," Petrobras chief executive Aldemir Bendine said.

An investigation into the corruption, known as Operation Car Wash because of one of the businesses allegedly involved, led the company to temporarily block ties with important suppliers, which include some of the country's largest construction companies, including Odebrecht SA and Andrade Gutierrez. The chief executives for those two companies were arrested last month as part of the investigation and charged with corruption and money laundering.

Both Odebrecht and Andrade Gutierrez have denied wrongdoing by the companies and their executives.

International suppliers were also implicated in the scandal. Prosecutors said that the shipbuilding arm of South Korean conglomerate Samsung paid bribes to a former executive at Petrobras, and they also have accused Swedish builder Skanska AB of taking part in the corruption at Petrobras. Samsung and Skanska officials didn't immediately respond to a request for comment.

Previously, Skanska has said it has a zero-tolerance policy against corruption and takes the situation seriously. Last July, Skanska announced it would shut its Latin America operations.

Earlier this week, authorities accused former Petrobras services director Renato Duque, who was arrested earlier this year for allegedly taking part in the scheme and is currently in prison, of accepting bribes from Joã o Bernardi, a sales representative for the local unit of Italian oil company Saipem.

Mr. Bernardi's lawyer couldn't be located, while a spokeswoman for Saipem said the company has yet to be contacted by Brazilian authorities and would cooperate fully if it does.

At the news conference to announce its new supplier controls Friday, Petrobras was joined by Brazil's top prosecutor, Rodrigo Janot, who said close to 140 million Brazilian reais ($41.17 million) had been returned to Petrobras from former executives. The return of the money had previously been announced.

"Today, Brazil´ s Justice shows that there is no citizen above the law," Mr. Janot said. "These criminals brutally looted resources from the company and took away pride from the Brazilian society."

In April, Petrobras put a tag price on the corruption scandal by writing off $2 billion in losses related to bribery. The company said it still hopes to get this money back.

Carlos Melo, political analyst at Insper, said Brazil needs to learn from past mistakes and be more vigilant about its state-owned companies.

"Institutional mechanisms are needed, but it is necessary to go beyond, creating a general law of state-owned companies, making sure that boards are effective and work with transparency and keeping agencies vigilant, " Mr. Melo said.

Write to Luciana Magalhaes at luciana.magalhaes@dowjones.com and Rogerio Jelmayer at rogerio.jelmayer@wsj.com

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