BRASILIA (Reuters) - Brazil's top prosecutor requested that President Dilma Rousseff be investigated for trying to obstruct a sweeping corruption investigation involving state-run oil firm Petrobras, local media reported late on Tuesday.
An investigation could well mark the political end for the beleaguered leader of the world's seventh-largest economy as it would be the first time that Rousseff would be directly implicated in Brazil's biggest-ever graft case.
She is already likely to be suspended from office as early as next week on unrelated charges of breaking budgetary laws.
The corruption scandal casts a shadow over 13 years of Workers Party rule that saw Brazil's middle class expand by some 40 million people since 2003 with the help of new social programs.
Rousseff has consistently maintained she has done no wrongdoing, despite serving as the chairwoman of Petrobras' board for several years when much of a billion-dollar kickback scheme played out.
The case has already seen executives from Brazil's biggest construction firms jailed and convicted for siphoning funds from Petrobras to bribe politicians. Around 50 politicians are under investigation, including the leaders of both houses of congress.
Neither Brazil's Supreme Court, which must authorize any investigation into Rousseff, nor the office of Prosecutor-General Rodrigo Janot returned calls and emails requesting confirmation of the request for investigation.
Globo News, Brazil's largest media conglomerate, along with the Estado de S.Paulo and Folha de S.Paulo newspapers reported the request made by the prosecutor at close to midnight on Tuesday.
The request will be analyzed by Supreme Court justice Teori Zavascki and is not public because it is based on recorded phone calls between Rousseff and former President Luiz Inacio Lula da Silva, news site G1 reported.
Federal Judge Sergio Moro in March made public taped phone conversations between Rousseff and Lula that fed opposition claims that Rousseff had tried to name Lula as her chief of staff in order to shield him from prosecution.
Newspaper Estado de S. Paulo also reported on Tuesday that Janot had charged Lula with participating in a scheme to stop former Petrobras executive Nestor Cervero from collaborating with the investigation. The federal prosecutors' office would not confirm the charge.
The Supreme Court did confirm that Janot had asked for Lula and several of Rousseff's ministers to be formally investigated, including Chief of Staff Jaques Wagner, the minister in charge of legislative affairs, Ricardo Berzoini, and Rousseff's spokesman, Edinho Silva.
Janot is expanding the investigation largely because of testimony from Senator Delcidio do Amaral, who decided to collaborate with the investigation in exchange for a lighter sentence. Amaral has said both Lula and Rousseff knew about the scheme.
Janot's requests add to a growing uproar over just how many senior politicians are suspected of taking kickbacks from Petroleo Brasileiro SA, as Petrobras is formally known (PETR4.SA).
Senior politicians will likely continue to face legal problems, and possible jail terms, well past Rousseff's expected ouster. Brazil's Senate this month will weigh her suspension ahead of a trial on charges she manipulated public accounts.
The lower house of Congress voted overwhelmingly to impeach her last month. Rousseff says she has done nothing wrong.
Rousseff's unpopularity mounted as Brazil fell into its worst recession in decades through what critics call her heavy-handed state intervention in the economy as a commodities boom went bust.
Asked if he would avoid inviting anyone under investigation to be a minister in any government he is asked to lead, Vice President Michel Temer, first in line for the presidency, said in a television interview on Tuesday he was unsure.
Prosecutors said in documents obtained by Estado de S.Paulo they did not see a reason to open an investigation of Temer, although he had been mentioned in plea bargain testimony. Janot said in the documents the "criminal organization" operating at Petrobras would not have been possible without Lula.
Lula's institute said on Tuesday Janot had offered a hypothesis without proof.
Rousseff's spokesman Silva, who was also the treasurer of the 2014 re-election campaign whose finances have been called into question for possibly benefiting from the Petrobras scheme, said in a statement the campaign was clean.
Prosecutors in the southern city of Curitiba have also sought to investigate Lula. Their efforts have stalled as the Supreme Court weighs whether or not Rousseff can make him a minister, a move that would give him immunity from all but the high court.
Reporting by Maria Carolina Marcello and Anthony Boadle; Writing and additional reporting by Caroline Stauffer and Brad Brook; Editing by Andrew Hay, Sandra Maler and Simon Cameron-Moore