A policeman stands in front of the Petrobras headquarters during a protest in Rio de Janeiro 4 March 2015 REUTERS/Sergio Moraes

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.

Luiz Fernando Pezao
Luiz Fernando Pezao, governor of Rio state Buda Mendes/Getty Images

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.

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 levelled 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

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.

More to follow...