More details were to be given at a press conference on Thursday, the prosecutor’s office said.

A judge must still formally accept the charges for the case to proceed.

Lula, who founded the ruling Workers‘ Party and was president between 2003 and 2010 before helping in his successor President Dilma Rousseff, has repeatedly denied ownership of the apartment or any impropriety.

The state prosecutor’s allegations come on top of a separate, much broader federal probe called Operation Car Wash which has uncovered a massive corruption scheme centered on giant state oil company Petrobras.

Executives at Petrobras allegedly took bribes in exchange for giving contracts to big construction firms and other contractors, who then massively overbilled the oil company. Politicians from several parties, including the Workers‘ Party, joined the sprawling scam, with bribe money feeding into campaign coffers, Operation Car Wash prosecutors say.

The corruption scandal, which has already seen a Who’s Who of Brazilian politicians and businessmen face charges, is believed to be the biggest ever in Brazil.

Lula is now the highest profile figure to be snared. Police briefly detained Lula for questioning last Friday and Car Wash prosecutors said they suspected that the triplex apartment was given to him as a bribe by OAS, one of the companies accused of participating in the Petrobras conspiracy.

Lula‘s lawyer, Cristiano Zanin Martins, told Folha de Sao Paulo news site that the state allegations “confirm the lack of impartiality with which this matter is being conducted.”

“Ex-president Lula is not the owner of the triplex,” Lula’s foundation said separately. “He has presented his defense and documents which prove this.”

The intensification of the legal push against Lula comes just before nationwide opposition rallies Sunday. Huge crowds are expected in the capital Brasilia, Rio de Janeiro and Sao Paulo to call for Rousseff to leave office.

Brazil‘s first woman president faces multiple problems.

Congress is mulling impeachment proceedings over alleged illegalities in the government’s budgetary maneuvers. Meanwhile, the Supreme Electoral Court is considering a case that could, eventually, result in judges declaring Rousseff‘s 2014 reelection to a second term invalid.

So far, Rousseff has managed to fight off impeachment, but the opposition has been fired up by the case against Lula and hopes that Sunday’s protests will send a powerful message to any waverers in Congress.

Analysts say that Rousseff could also be in the sights of Operation Car Wash prosecutors.

She has not been directly accused of any wrongdoing, but was chairman of Petrobras during much of the period when the corruption took place. A Brazilian magazine report -- that a Workers‘ Party senator accused in the scheme has promised to testify in a plea bargain that Rousseff tried blocking the investigation -- caused waves in Brasilia last week.