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Silvia Izquierdo, Associated Press
Revelers parade while holding fake Intravenous bottles with sings that read "Where is the money that was here?," "I'm Petrobras", "Honesty' and "Shame" during a carnival parade, in Rio de Janeiro, Brazil, Saturday, Jan. 31, 2015. Embattled Brazilian oil giant Petrobras said Wednesday that the company's chief executive officer and five other top figures stepped down amid a long-running and massive kickback scandal at the firm. Petrobras said in a one-line statement on its website that CEO Maria das Gracas Foster and five other executive directors were out.

RIO DE JANEIRO — Embattled Brazilian oil giant Petrobras said Wednesday that the company's chief executive officer and five other top figures stepped down amid a long-running and massive kickback scandal at the firm.

Petrobras said in a one-line statement on its website that CEO Maria das Gracas Foster and five other executive directors were out. There have been loud calls from business and political circles for months for the resignation of the company's top officials after news of the alleged corruption scheme broke.

The oil firm lost billions in market value in the past year as daily reports broke news about the extent of the alleged corruption scheme. Prosecutors say at least $800 million in bribes were paid by construction and engineering firms in return for inflated contracts worth billions.

Aside from its market value, Petrobras has seen its debt downgraded by both Moody's and Fitch in the past week, further choking its ability to borrow on international markets.

Petrobras is Brazil's biggest company and is in charge of tapping big offshore oil fields and creating wealth that leaders hope will propel the country to developed world status. But the debt-plagued firm hasn't met development goals, and the riches remain buried deep under the sea.

The company's statement said in English that its board of directors on Friday "will elect new executive board members" after the resignation of Foster and five other executive directors.

Petrobras, one of the globe's leading offshore companies that in recent years discovered massive offshore oil fields that could hold up to 100 billion barrels, has been mired for months in a corruption case involving former company executives as well as the heads of many of Brazil's main construction companies.

Brazilian prosecutors have said the kickback scheme involved at least $800 million in bribes and other illegal funds. They expect that figure to grow as they keep investigating. Some of that money was funneled back to the ruling Workers' Party and its allies campaign coffers, often as legal corporate donations.

Federal prosecutors said they've recovered about $170 million involved in the scheme, that over 230 businesses of all sizes are being investigated and that 86 people are facing charges so far, including several top executives from Brazil's main construction and engineering firms who have been jailed.

Additionally, federal prosecutors are expected to announce charges this month against dozens of politicians, mostly congressmen, in connection to the case.

Speculation has been rife that Foster, 61, would be fired, but her friend and ally Brazilian President Dilma Rousseff sharply defended her record of over three decades in the company.

The pressure from political and business circles to find new leadership at Petrobras increased last week after the company belatedly released an unaudited earnings report that didn't include an estimate on losses due to corruption.

Foster then told reporters two days after the earnings report was released that losses on the books due to inflated contracts could be over $30 billion — a preliminary calculation that reportedly infuriated Rousseff.

Rousseff, a former energy minister and presidential chief of staff who herself served as chair of the Petrobras board for seven years through 2010, is widely seen as wanting a replacement from outside the company, but the ongoing scandal is thought to be making the top position a hard sell to prospective candidates.

According to the Folha de S.Paulo daily, which first broke the news Tuesday of Foster's imminent departure, Rousseff's predecessor and influential mentor, Luiz Inacio Lula da Silva, has suggested two possible replacements for Foster: the former head of Brazil's Central Bank, Henrique Meirelles; and the CEO of mining giant Vale, Murilo Ferreira.

In a research note late Tuesday, the U.S.-based Eurasia Group wrote that "we expect whoever to come on board to have strong market credentials."

"The presidential palace has for some time viewed Petrobras's corruption scandal as a macro risk to growth, and as such, a premium will be placed on nominating a CEO and board members that generate a credibility punch," the note added.

Fabio Funzetti, a Sao Paulo-based oil analyst for Antares Capital Management, said Wednesday's decision was inevitable but a little too late.

"Petrobras is in an unsustainable position," he said. "They have to start to turn things around in a very significant way. It's performing in a very worrisome way. Petrobras is in dangerous levels of debt."

Shares of Petrobras soared 15 percent on Tuesday amid rumors that Foster was on her way out. Shares were down 1.5 percent at midday Wednesday as investors took profits.

Associated Press writer Adriana Gomez contributed to this report.