Rio de Janeiro, March 18 (IANS): Brazil's opposition has announced that it will ask the Supreme Federal Court to investigate President Dilma Rousseff for the Petrobras corruption scandal in which her party's treasurer Joao Vacarri is also implicated, Efe news agency reported.

The investigation petition, to be made later on Wednesday, brought together four main opposition groups, namely Brazilian Social Democracy Party, Popular Socialist Party, the Democrats and Solidarity party, who were encouraged by mass protests against Rousseff on Sunday.

Two weeks ago, the Supreme Court ruled out investigations against Rousseff after Brazilian Attorney General Rodrigo Janot argued that the president can only be charged for actions carried out during his or her presidency.

During the investigations, Rousseff was named by a former senior Petrobras official as an indirect beneficiary in the corruption network.

However, these incidents allegedly occurred before 2010 when she was not the president.

Another factor that encouraged the opposition was the imputation of the treasurer of Rousseff's Workers' Party (PT) after he was charged by the Public Prosecutor's Office on Monday for his involvement in the scandal.

PT president Rui Falcao defended Vacarri's innocence and said that he would continue to retain his position.

He further said that the treasurer would be dealt with according to the norms of the party if he was found guilty of illegal transactions.

The Petrobras bribes were disguised as legal donations for the electoral campaigns of PT, according to the Attorney General's Office.

According to the police, businessmen conspired to earn contracts with Petrobras at inflated prices, and are alleged to have shared part of their corrupt earnings with state directors of Petrobras politicians.

The prosecution estimates that around $646 million were diverted from Petrobras' coffers.

Police arrested five former Petrobras officials, two of whom accepted their guilt and named others who were party to the crime in exchange for a reduced sentence.

Dutch firm SBM Offshore, under investigation for allegedly bribing Petrobras for contracts, said on Wednesday that they were negotiating with Brazilian authorities about sharing information on the case.

The Petrobras corruption scandal has strongly hit Rousseff's popularity, which is at its lowest since she was elected president in 2011.

The scandal was responsible for wide scale protests on Sunday, bringing together more than a million people in different cities of the country.

In response to these protests, Rousseff had promised to present to the Congress a series of anti-corruption measures, which were announced Tuesday by Justice Minister Jose Eduardo Cardozo.

The content of the proposals will be detailed by Rousseff on Wednesday when the bill will be presented before the Chamber of Deputies, Cardozo said.

The opposition has criticised these measures, claiming that they lack credibility as it was Rousseff's own party that is under investigation.

A new scandal emerged on Tuesday when the Brazilian police uncovered a network that allegedly diverted around $31.2 million to Caixa Economica Federal, the second largest public bank of Brazil.