Petrobras gasoline is offloaded at a gas station of Brazil's government-run oil company Petrobras on February 5, 2015 in Rio de Janeiro, Brazil. Mario Tama/Getty Prosecutors have announced that they will investigate three members of the Brazilian ruling coalition in connection with the corruption scandal enveloping state oil giant Petrobras, including the governor of Rio de Janeiro state.

Investigators into widespread corruption at Petrobras dubbed "Operation Lava Jato" (Portuguese for Car Wash), have already made dozens of arrests, including 47 politicians, former Petrobras executives and several third-party company directors.

This week, the President of the Senate, Senator Renan Calheiros, and the President of the House of Representatives, Eduardo Cunha, were included on the list of personalities under suspicion over a scheme facilitating corruption and money laundering that saw an estimated $3.8bn (£2.6bn) creamed off inflated contracts over a decade.

The latest to fall under suspicion in the widening so-called 'Petrolão' scandal are three members of the ruling coalition: Luiz Fernando Pezao, Governor of Rio state, his predecessor Sergio Cabral, and Tiao Viana, Governor of Acre state, in Brazil's north.

Petrobras' officials look at oil platform P-52 which is in the final stage of the construction for the state-run oil company Petrobas at Brasfels' shipyard in Angra dos Reis, Brazil, Thursday, Aug. 3, 2006. AP A statement from the attorney-general's office said it had "detected evidence of passive corruption and money laundering" against the three men.

The accusations leveled against them were made by Paulo Roberto Costa, a former Petrobras director who turned whistleblower in a bid to reach a plea bargain with investigators.

Nobody has yet been convicted.

Embarrassment for Brazil's president

Brazil's Senator and former president Fernando Collor de Mello speaks during an interview in Brasilia, Brazil, Friday July 8, 2011. (AP Photo/Eraldo Peres) AP A former president of Brazil has also been accused of taking a $1m bribe from the embattled Petrobras.

Fernando Collor de Mello, who was president from 1990 to 1992, is accused of receiving $1.05m from a $105m deal signed by BR Distribuidora, a subsidiary of Petróleo Brasileiro, as Petrobras is known.

The revelations could be of further embarrassment to governing political parties, such as incumbent President Dilma Rousseff's Brazilian Labor Party (PTB), which also publicly refuted the claims and reiterated its support for the former president.

While witnesses have alleged the PTB benefited financially from the scheme, Rousseff has repeatedly denied all knowledge of corruption at Petrobras, despite the fact that she was on the board of directors while much of the graft is alleged to have taken place.

Calls are growing to impeach Rousseff, who was re-elected in October 2014. A petition on campaigning website Avaaz with this motive is gaining traction as the politician faces a major political crisis.