A sharply divided top court voted early Thursday to reject an attempt by former Brazilian President Luiz Inacio da Silva to stay out of jail while he appeals a corruption conviction, delivering a hard blow to the front-running candidate in this year's presidential election in Latin America's largest nation.

After nearly 11 hours of often heated debate, the Supreme Federal Tribunal voted 6-5 to deny da Silva's request to stave off a 12-year prison sentence while he fights a conviction that he has always argued was nothing more than a ploy to keep him off of the October ballot.

Despite the conviction and several other corruption charges against him, da Silva leads all preference polls for the election.

The decision means that da Silva will likely be jailed soon, though probably not until at least next week thanks to various technicalities.

Chief Justice Carmen Lucia, who was sharply criticized during the session by various colleagues, cast the deciding vote after the court was tied at 5 to 5.

"The constitution secures individual rights, which are fundamental to democracy, but it also assures the exercise of criminal law," she said.

The debate at the Supreme Federal Tribunal underscored how fraught the matter is at a time of high tension and angst in Brazil.

Justice Gilmar Mendes, traditionally a critic of da Silva, voted in favor of da Silva's petition to stay out of jail, challenging his colleagues to buck pressure from society.

"If a court bows (to pressure), it might as well not exist," said Mendes.

Justice Luis Roberto Barroso argued that the integrity of the justice system was at stake.

"A penal system that doesn't work with minimal effectiveness leads to an instinct for taking justice into one's own hands," Barroso said in voting against da Silva.