Opponents of the new government installed by acting president Michel Temer have accused it of seeking to smother the anti-graft probe known as "Operation Car Wash," which has uncovered a multi-billion-dollar embezzlement and bribery scheme centered on state oil company Petrobras.
But Justice Minister Alexandre de Moraes said he would protect the probe's independence and even increase its funding if necessary.
"There isn't the slightest possibility of interference," said Moraes, who was previously security secretary for the state of Sao Paulo.
Temer, the former vice president, took power on Thursday from his suspended boss-turned-nemesis, Dilma Rousseff, pending her impeachment trial on unrelated charges of cooking the government's books.
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He promptly sacked the leftist leader's ministers and installed his own business-friendly cabinet -- including three ministers under investigation in the Petrobras probe and several others whom witnesses accuse of involvement.
Temer is not under investigation himself, but some key allies are, including top leaders in his party, the center-right PMDB.
"The law must apply equally to everyone, regardless of name or party affiliation," he said.
Moraes is one of several controversial figures in Temer's cabinet, which supporters of Rousseff, Brazil's first female president, attacked as a throwback to another era because its members are all conservative white males.
Dubbed "Temer's pit bull," Moraes oversaw a police force accused of frequent human rights abuses in Sao Paulo, including the use of death squads to confront suspected criminal groups.