Rio de Janeiro (AFP) - A Brazilian court cleared ex-president Luiz Inacio Lula da Silva Friday to start work as chief of staff to his embattled successor Dilma Rousseff, overturning an injunction blocking his appointment.

But Lula still faces a flurry of other court challenges to his nomination, which opponents reject on grounds that he faces corruption charges and is suspected of seeking ministerial immunity to avoid arrest.

Government lawyers have asked the Supreme Court to issue a definitive ruling putting the 12 cases before it to rest.

Rousseff says she needs her mentor, "the greatest politician in Brazil," to help her deeply embattled government, which is fighting an explosive corruption scandal, a deep recession and the splintering of its coalition.

But hours after the leftist president swore him in Thursday, a federal court in Brasilia blocked Lula from taking up his functions over suspicions that he and Rousseff were trying to obstruct the course of justice in the very same corruption case.

Lula is charged with accepting a luxury apartment and country home as bribes from companies implicated in a multi-billion-dollar graft scheme at state oil company Petrobras.

The initial injunction against Lula was overturned on appeal, only for another federal court, in Rio de Janeiro, to issue a similar ruling.

In all, some 50 cases have been filed against Lula's appointment in courts at different levels, according to the government's lawyers.