BRASILIA, March 6 (Xinhua) -- Brazil's Superior Court of Justice on Tuesday rejected a habeas corpus petition to scrap ex-President Luiz Inacio Lula da Silva's prison sentence.

The five-judge panel's unanimous decision marks another legal setback for the popular Lula, who has already lost several appeals against a corruption conviction that threatens to derail his hope of running in the October presidential elections for a third term.

Judges disagreed with the argument that the legal process against him was flawed, effectively upholding his 12-year prison sentence.

However, the decision "does not send Lula straightaway to jail, as the former president still has a petition under consideration by an appellate court," online news agency Agencia Brasil said.

Lula was convicted of corruption for accepting a luxury beachfront apartment from construction firm OAS in exchange for lucrative contracts for state oil giant Petrobras.

Polls have consistently showed Lula as Brazilians' favorite potential candidate despite the conviction, which he claims is politically motivated to sideline his presidential aspirations.