Rousseff under increasing pressure as party official arrested

Moves by Brazil's opposition to open impeachment proceedings against President Dilma Rousseff have intensified following the arrest of the treasurer of her ruling Workers Party as part of the investigation into corruption at state-controlled oil giant Petrobras.

João Vaccari was picked up in São Paulo by federal police on Wednesday after a judge ordered his detention saying it was necessary to prevent possible interference with the investigation. He was flown to the southern city of Curitiba where he joins 19 others already in detention for their role in the scandal, among them former Petrobras executives, businessmen and black market financiers.

Investigators have gathered evidence that Mr Vaccari raised hundreds of millions of euro for the Workers Party from companies in exchange for Petrobras contracts. Key to their case has been evidence provided by others already charged as part of plea-bargain deals. An executive from Camargo Corrêa, one of Brazil's biggest construction groups and a key Petrobras contractor, has told prosecutors that Mr Vaccari had companies disguise bribes paid for contracts in the form of legal donations.

Mr Vaccari’s arrest brings the investigation closer to the party’s top leadership as Mr Vaccari was responsible for raising and distributing funds for Ms Rousseff’s re-election campaign last year. She has said she is “certain” no funds that were the result of bribery were used in her campaign.

The Workers Party's president Rui Falcão held an emergency meeting with former president Luiz Inácio Lula da Silva after the arrest. In a statement afterwards the party said Vaccari had asked to temporarily step down from his role as treasurer. Mr Falcão described the arrest as "unnecessary" and "unjustified".

Mr Vaccari has always denied any wrongdoing but prosecutors are also looking into signs that his wife, daughter and sister-in-law illicitly enriched themselves.

News of the arrest of a senior Workers Party figure has reinforced those among the country’s political opposition who are demanding that congress open impeachment proceedings against Ms Rousseff.

Support for the move was seen to have weakened after pro-impeachment protests on Sunday were noticeably less well attended that rallies held a month ago. But following Vaccari’s detention the Social Democrats, Brazil’s largest opposition party, moved to join five smaller groupings in drawing up a formal request for congress to install impeachment proceedings.

Party elders have opposed the move, arguing material evidence to link Ms Rousseff to wrongdoing was still lacking. But younger deputies are increasingly determined to push for the measure which a recent opinion poll shows is backed by 63 per cent of Brazilians.

As well as undermining Ms Rousseff the scandal has caused havoc in Brazil’s oil sector. Petrobras has been forced to suspend payment on contracts with companies caught up in the investigation leading several to enter bankruptcy protection.

One of Mr Vaccari's predecessors as Workers Party treasurer, Delúbio Soares, was sentenced to six years and eight months in jail for his role in the mensalão vote-buying scandal during Lula's presidency. He served ten months before being released to serve the remainder of his time under house arrest.