New investigations against the former presidents could spell longer prison terms for Luiz Inacio Lula da Silva and Dilma Rousseff.

Brazil has opened criminal proceedings against former left-wing leaders Luiz Inacio Lula da Silva and Dilma Rousseff for allegedly receiving bribes with money diverted from state-owned oil giant Petrobras.

The Workers Party (PT) of the two ex-presidents has strongly denied the charges, calling them a "scandalous maneuver" with partisan motives.

In addition to Lula and Rousseff, the PT's current president and several former ministers are implicated.

Attorney General Rodrigo Janot filed a complaint last year alleging the accused conspired to form a criminal organization that received 1,480 million reais (now $390 million) of bribes in money diverted from the state.

His filing was accepted by the Federal Court on Friday, which asked the accused to present their defence within 15 days.

They are the first criminal charges to be brought against Rousseff, who came to power in 2010 and was re-elected in 2014 before being impeached in 2016 for allegedly manipulating public accounts.

Lula is currently serving a 12-year-sentence for accepting a seaside apartment as a bribe during his 2003-10 presidency.

He also has at least three other proceedings before the courts, pleading innocent to all the charges and denouncing them as political persecution.