Lawyers for former Brazilian president Luiz Inacio Lula da Silva on Saturday criticized the fourth corruption case brought against him after a judge accepted formal charges that he had interfered in a government tender to buy new fighter jets.

Lula, who was no longer president when the alleged illegal practices happened, was accused of using his influence over his successor's government to help Swedish plane maker Saab AB win the tender for 36 jets worth around $5.6 billion.

The former presidents' lawyers said he had no role in the selection of the Saab Gripen fighter jets in December 2013 and obtained no illicit gains related to the deal.

They said Lula's son, Luis Claudio Lula da Silva, who is accused in the case of receiving 2.5 million reais ($740,000) in exchange for his father's influence, was paid for sponsorship of an American football tournament he organized in Brazil.

The mounting charges against the former president underscore the sweeping nature of nearly three years of corruption investigations that have spared few in Brazil's political establishment, adding to uncertainty about the 2018 presidential election.

The latest polling shows Lula among the leading candidates in the 2018 race, though the number of respondents rejecting his potential candidacy rose to 44 percent in the latest Datafolha poll. The head of the leftist Workers Party reiterated this month that Lula will be the party's candidate in 2018 and there is no plan B.

Saab responded to the charges against Lula this month by saying it had rigorous policies controlling its business relationships and highlighted that the company and its representatives were not facing any charges.

A representative for Saab in Brazil did not immediately respond to a request for comment on Saturday.