"I think this does not place the government under any suspicion, as nobody in the government has been officially accused of anything," Rousseff said in comments made Sunday and carried by newspapers on Monday.

The scandal at Petrobras erupted on Saturday with polls already showing Rousseff likely to lose the upcoming presidential elections to environmentalist Marina Silva in a run-off October 26.

Jailed former Petrobras director Paulo Roberto Costa has alleged that dozens of leading politicians received kickbacks on Petrobras deals.

Costa was arrested last March on suspicion of corruption and money laundering while he was head of Petrobras' refining and supply between 2004 and 2012.

He is reportedly trying to strike a plea deal with prosecutors in return for a reduced sentence.

Rousseff also ordered Justice Minister Jose Eduardo Cardozo to ask federal police to get her the list of people named by Costa.

"If they do not give it to me, I am going to ask the supreme court," the president told reporters,

Conservative magazine Veja, which first disclosed the allegations, said that among those named by Costa were Energy Minister Edison Lobao, Senate President Renan Calheiros, Enrique Eduardo Alves, chairman of the chamber of deputies, and ruling Workers Party (PT) treasurer Joao Vaccari Neto.

Globo daily quoted Rousseff as saying she was awaiting the results of the investigation into the allegations before commenting further.

Rousseff is now fighting to regain the initiative from Silva, who has surged in the polls since the sudden death of Brazilian Socialist Party candidate Eduardo Campos.

Campos was killed in a plane crash August 13, clearing the way for Silva, his vice presidential running mate, to take his place at the top of the Socialist ticket.

But Veja said Costa also named Campos as having benefited from the Petrobras kickbacks, complicating matters for Silva, who hotly denied the allegation as a slur.

Seeking to breathe new life into her campaign, Rousseff at the weekend appointed a new campaign coordinator, Minister of Agrarian Development Miguel Rossetto.

Rossetto replaced Rui Falcao, chairman of the PT, which has been in power since 2003.

As Rousseff and Silva contend with the emerging fallout of the Petrobras graft case, social democratic candidate Aecio Neves, running a distant third in the presidential poll, said at the weekend it was inconceivable Rousseff "knew nothing" of the alleged kickbacks.