BRASILIA (Reuters) - Former President Luiz Inacio Lula da Silva on Tuesday called charges “false” that he tried to block an ongoing investigation of the biggest graft scandal in Brazil’s history, which helped end the 13-year rule of his leftist Workers Party.

Former Brazilian President Luiz Inacio Lula da Silva gestures as he attends a Workers Party National congress in Sao Paulo, January 19, 2017. REUTERS/Leonardo Benassatto

Addressing a packed court, a defiant Lula appeared for the first time in one of five corruption trials in which he is a defendant and whose outcomes could determine whether the former president, still Brazil’s most popular politician, could return to the top office in Latin America’s biggest country.

With chanting supporters outside, Lula said he had nothing to do with an attempt to pay a former executive at Petrobras, the state-run oil company at the center of the scandal, in exchange for the executive not testifying in the investigation.

“The facts are false,” the 71-year-old former union leader told the federal court in Brasilia in a one-hour hearing, at times banging the table with his fist in anger. Outside, a group of 50 supporters chanted “Brazil, urgent, Lula for president.”

Lula, president from 2003-2010, is a front-runner for the 2018 presidential election. Although the corruption trials could legally bar him from running if he is convicted and it is upheld by an appeals court, the Workers Party plans to launch his candidacy in April.

“They have invented accusations against me and made up plea bargain statements,” Lula said, criticizing much of the testimony obtained from other defendants in exchange for leniency in the scandal.

He characterized his prosecution as politically motivated and an insult to a two-term leader who presided over an economic boom, left office with approval ratings of nearly 90 percent and helped raise Brazil’s standing on the world stage.

Delcidio Amaral, a former Workers Party senator who was jailed in the probe, said in a plea deal that Lula had instructed him to bribe Nestor Cervero, the Petrobras executive, to keep him from collaborating with prosecutors. The offer, in which Amaral promised money and an escape from Brazil, was secretly taped by Cervero’s son.

“I had no reason to fear a Cervero plea deal,” Lula said.

If convicted of obstruction of justice, Lula could face a prison sentence of 3 to 8 years. He faces more serious indictments on charges of accepting gifts from engineering companies involved in the Petrobras scandal.

A poll last month showed Lula winning a projected run-off against his likely rivals next year. Previous surveys forecast his defeat in a second round.