Former president Luiz Inacio Lula da Silva's ex-chief of staff has come under scrutiny from prosecutors investigating a massive kickback scandal at Brazil's state oil giant Petrobras, local media reported.

Jose Dirceu, Lula's onetime right-hand man, was convicted in 2012 and sentenced to more than seven years in prison for a corruption scandal involving payoffs to Brazilian lawmakers, known as the "Mensalao."

Globo television network reported Thursday that investigators determined three construction companies implicated in the separate four billion dollar Petrobras scandal made $1.3 million in payments to a consulting firm Dirceu owned with his brother.

The construction companies -- Galvao Engenharia, OAS and UTC Engenharia -- are suspected of being part of a cartel that made under-the-table payments to Petrobras directors in return for lucrative contracts.

Like the earlier "Mensalao" scandal, the corruption at Petrobras is also alleged to have involved payments to politicians, although none have been charged.

A former Petrobras director, Paulo Roberto Costa, who has been jailed in the scandal, has said dozens of politicians benefited from kickbacks paid over a decade.

President Dilma Rousseff chaired Petrobras from 2003 to 2010, coinciding with a period the kickbacks were being taken. She denies any knowledge of the scheme.

Investigators are looking into whether JD Assessoria e Consultoria, Dirceu's company, was a conduit for bribes, Globo said.

The company said in a statement Thursday that the payments it received were for legitimate consulting services on development opportunities in Latin America and Europe.

Dirceu was forced to resign as Lula's chief of staff in 2005 after the "Mensalao" scandal broke, exposing payments to lawmakers for votes.

Dirceu has been under house arrest since November, serving his seven year and 10 month sentence.