A Brazilian prosecutor has asked the Supreme Court to investigate 54 people, including a clutch of politicians, over a deepening corruption case that has rocked Petrobras, the nation's largest corporation.

The growing scandal, which investigators have dubbed Operation Car Wash, concerns kickbacks estimated at $3.8bn at Petrobras, a state-owned oil giant.

The crisis has become a major headache for President Dilma Rousseff - who chaired the Petrobras board from 2003 to 2010, during much of the period when the scheme allegedly operated - and her increasingly embattled government.

"There have been 28 requests for new investigation files ... which involve 54 people," a spokesman for prosecutor general Rodrigo Janot told the AFP news agency.

The spokesman had initially indicated that all 54 were politicians - meaning they would have immunity - but later clarified only some were, while the rest had connections to politicians.

The names of those who will be placed under investigation if the court gives the go-ahead will not be revealed for the time being.

News site Globo quoted the Estado de S Paulo newspaper as saying several former ministers, current and former state governors and Congressmen were among the 28 politicians being investigated.

Those identified in the media over recent months have all denied wrongdoing.

Service contracts 

Federal prosecutors indicate about two dozen companies, mainly top construction firms, paid massively over the odds for service contracts with Petrobras, with up to three percent creamed off in corrupt payments to politicians, mainly government allies. 

Brazil's public prosecution service last month urged the firms caught up in the decade-long scandal to pay $1.5bn in damages as well as yet-to-be-specified fines.

Authorities are questioning a number of former Petrobras and construction firm executives after one former executive at the oil firm blew the whistle on the scheme a year ago. He is seeking a plea bargain with investigators.

Some of those questioned by police as they seek to have their potential sentences reduced say the kickbacks were paid into politicians' personal bank accounts or into party coffers.

The list of names handed over to the Supreme Court by Janot opens a new phase in the investigation given the potential ramifications for politicians, while Petrobras itself has seen its reputation take a dramatic dive.

Last week, Moody's rating agency downgraded the company's stock into junk territory - a fourth downgrade in as many months with Petrobras not just embroiled in the kickbacks fallout but having failed to release verified 2014 earning results.

The firm says it will do so only in May and says it will have to cut back its investment budget for this year by $10bn.

Source: AFP