Cardozo is set to take the position of attorney general instead, President Dilma Rousseff's office said in a statement on Monday. The post is not involved with criminal investigations and prosecutions.

His resignation is believed to be connected with the massive corruption probe into the state oil company Petrobras.

The company has said it lost more than $2 billion (1.84 billion euro) due to charges of price-fixing, bribery and kickbacks in a long-running graft scheme. Also, various construction and engineering firms are suspected of paying at least $800 million in bribes to politicians and executives for lucrative Petrobras contracts.

Government opponents accuse President Rousseff of financing her 2014 campaign with graft money. Rousseff's popular predecessor, Luiz Inacio Lula da Silva, also faces questions over disputed ownership of a beach-front penthouse triplex and country estate.

The investigation has already placed several ruling Workers' Party members behind bars. Last week, Rousseff political consultant Joao Santana was arrested, with prosecutors alleging that he was paid with money siphoned from Petrobras.

Rousseff, who was the chairwoman of the Petrobras board between 2003 and 2010, has denied any wrongdoing.

Police protest pressure on Cardozo

The Workers' Party officials have complained about Cardozo's refusal to limit the scope of the investigation, calling the corruption investigations a political witch-hunt. In turn, Cardozo stated he could not interfere without evidence that police violated a person's rights.

On Monday, a group of police chiefs expressed "extreme concern" at Cardozo's departure, arguing it was a result of political pressure to limit their probe.

Brazil's biggest opposition party, the PSDB, has already asked the country's top electoral court to annul Rousseff's 2014 re-election. Any evidence of illegal financing would boost their claim and raise the stakes in the current political crisis.

dj/gsw (Reuters, AP)