BRASILIA (Reuters) - Brazil’s top prosecutor recommended on Thursday that the Supreme Court block the appointment of former president Luiz Inacio Lula da Silva as cabinet minister because it was intended to disrupt a corruption investigation.

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Lula’s protégée and successor, President Dilma Rousseff, last month named him to be her cabinet chief, ostensibly to help her raise dwindling support among her coalition allies to fight off the threat of impeachment in Congress.

The appointment would have given Lula some immunity from prosecution by crusading anti-corruption lower court Judge Sergio Moro because ministers and elected officials can only be tried by the Supreme Court in Brazil.

A recording made public by Moro of a telephone conversation between Lula and Rousseff discussing the appointment appeared to confirm that they were seeking to shield the Workers’ Party leader from prosecution and possible arrest in a graft probe.

In his recommendation to the Supreme Court, Prosecutor General Rodrigo Janot said the cabinet appointment was intended to remove the investigation from the lower court judge and “disrupt” the corruption probe known as “Operation Car Wash.”

Lula is under investigation for allegedly benefiting, in the form of payments and a luxury seaside penthouse, from a massive graft scheme uncovered at state-run oil company Petrobras.

The widening investigation has caused a political storm that threatens to topple Rousseff, who is facing impeachment over an unrelated accusation of doctoring government budget accounts.

A Supreme Court judge suspended Lula’s appointment on March 18, arguing that it was an illegal move to shield him. The full court must rule on April 20 whether to uphold the injunction issued by Justice Gilmar Mendes.

It must also decide whether to return the Lula investigation to the lower court.

Lula, Brazil’s first working class president from 2003 to 2010, is still the country’s most influential politician, but the delay in his appointment limited his ability to help Rousseff weather the political crisis.