Brazilian prosecutors are filing charges against ex-President Lula da Silva in a money laundering investigation, officials say.

He denies any wrongdoing and says the charges are politically motivated.

The accusations are part of a major corruption investigation at the state oil company, Petrobras.

Lula and his wife, Marisa Leticia, face questions over the alleged ownership of a seafront penthouse in the exclusive resort of Guaruja.

They are among 16 people who are formally being accused of money laundering by Sao Paulo prosecutors.

Lula's son is also reported to be on the list.

The charges still have to be formally accepted by a judge.

Prosecutors have announced a news conference for later on Thursday.

Lula's lawyer, Cristiano Zanin Martins, said he was not given official access to the accusations against the former leader.

"This action confirms the bias [against Lula] in this whole process," he said.

Prosecutors say one of the country's biggest construction firms, OAS, carried out extensive refurbishment on the penthouse.

Officially the apartment belongs to OAS, which is under investigation. It has been accused of paying bribes to politicians and senior officials at Petrobras to secure lucrative contracts.

Lula, 70, denies all accusations and says he never owned the apartment. He also accuses the prosecutor in the case of being arbitrary, says the BBC's Daniel Gallas in Sao Paulo.

The former president was detained last Friday for questioning over the three-storey penthouse.

His high-profile detention led to criticism not only from his supporters but also from judges and politicians, who said the measure was unnecessary.

Lula's supporters say the attacks on him are aimed at tarnishing his reputation, amid rumours that he may run for office again in 2018.

He was Brazil's president from 2003 to 2011 and was succeeded in office by his political protege, Dilma Rousseff, who has record-low approval rates amid a serious economic crisis.

She joined hundreds of people showing support for the former president last Saturday.

Lula, a former factory worker and union leader, remains a very popular figure in Brazil despite the accusations against senior member of his left-leaning Workers Party.