Inflatable dolls known as "Pixuleco" depicting Brazil's former President Luiz Inacio Lula da Silva are seen during a protest against Brazil's President Dilma Rousseff's appointment of Lula da Silva as her chief of staff, at Paulista avenue in Sao Paulo, Brazil, March 17, 2016. [Photo/Agencies]

Only Brazil's Supreme Court has jurisdiction in cases against ministers. Shortly after the swearing-in ceremony, a federal judge in Brasilia issued an injunction against Lula's appointment on the grounds it blocked "the free exercise of justice."

Attorney General Jose Eduardo Cardozo vowed to appeal the injunction against Lula joining the government, which he called the decision of a partisan judge.

The standoff inflamed tensions that are already running high between Brazil's executive and judiciary branches, as the snowballing Petrobras probe reaches Rousseff's inner circle and hangs over a congressional impeachment committee named on Thursday.

Calls for Rousseff's impeachment have centered on allegations, unrelated to Petrobras, that she broke budget rules intentionally to boost spending as she campaigned for re-election in 2014. A 65-member impeachment committee of the lower house will now formally begin studying whether there are sufficient grounds to remove her.