Sergio Moro, Brazil's justice and security minister, resigned on Friday after clashing with President Jair Bolsonaro over the sacking of the federal police chief.
Moro, a former anti-corruption judge, hit out at "political interference" in the federal police, saying that he could not do his job without "autonomy" for the force.
The news sparked jitters in the markets with Sao Paulo's stock exchange, the largest in Latin America, plunging more than eight percent and the real dropping to a record low of 5.7 against the US dollar.
"I'm going to start packing up my things and send my resignation letter," said Moro, 47, during a long speech in the capital Brasilia in which he accused the far right Bolsonaro of "breaking the promise of a carte blanche."
The move came following Bolsonaro's sacking of federal police chief Mauricio Valeixo, a close Moro ally.
"The change at the head of the federal police without a genuine reason is political interference that harms my credibility and that of the government," said Moro.
Moro said Bolsonaro had told him he was replacing Valeixo because he wanted someone with whom he had "personal contact, who he could call, ask for information, intelligence reports."
"Providing this type of information is not the job of the federal police," he added, insisting that the independence of investigations needs to be preserved.
Moro revealed that Bolsonaro had said one of the reasons he wanted to replace Valeixo was that he was "worried" about some ongoing investigations.
Bolsonaro's decision to sack Valeixo against Moro's advice was "a signal that the president wanted me out," said Moro.
Sylvio Costa, the founder of specialized political website Congresso em Foco, said the president's move was about self-preservation.
"Bolsonaro wants to protect himself. It's the federal police that's investigating various suspected crimes haunting the president, his family and allies," said Costa.
'Politicization'
Last week, Bolsonaro also fired his health minister, Luiz Henrique Mandetta, who supported isolation as a tool to contain the spread of the virus. Bolsonaro has repeatedly downplayed the danger of COVID-19.
"Mandetta's vision was that of health, of life. Mine is more than life, it includes the economy and jobs," Bolsonaro said at the time.
Moro made his name as a judge in leading the high-profile Car Wash corruption investigation that notably saw former leftist president Luiz Inacio Lula da Silva jailed for accepting a bribe.
He began investigating leading political figures under a left-wing government in 2014 but said even then he'd never before faced such political interference.
Analysts say Moro's departure crowns a "politicization" process of governmental organs battling corruption despite Bolsonaro insisting during his 2018 election campaign that he would provide transparency and honesty.
"Since he assumed the government (in January 2019), Bolsonaro has tried to intervene in a series of anti-corruption organizations with the aim of increasing his control over future investigations," said Thomaz Favaro, an analyst for Control Risks consultancy.
Favaro pointed to Bolsonaro's choice of Augusto Aras as attorney general, despite him not figuring on a list suggested by Brazilian public prosecutors.
Picking from that list was a tradition that had been respected since at least 2003.
"Moro's resignation is a seismic event in Brazilian politics," said Ilona Szabo, executive director of the investigative Igarape Institute.
"His departure signals a dangerous new phase for Brazil. It amounts to a 'coup' against democracy because the autonomy of the federal police (and rule of law) is an essential foundation for democratic governance."