"I leave with this certainty: mission accomplished," Azevedo e Silva said in a brief statement, without giving a reason for his surprise departure.

Azevedo e Silva, a 67-year-old army reserve general, had been in the post since Bolsonaro took office in January 2019.

His announcement came hours after Foreign Minister Ernesto Araujo submitted his resignation amid controversy over the government's problems securing more Covid-19 vaccines.

Last week, Bolsonaro also replaced former health minister Eduardo Pazuello, another army general, with cardiologist Marcelo Queiroga, his fourth health minister of the coronavirus pandemic.

The president, who has long defied expert advice on the pandemic, is facing mounting pressure to contain a deadly surge of Covid-19 in Brazil and secure more vaccines for the country's 212 million people.

More than 312,000 people have died of Covid-19 in Brazil, according to official figures, the second-highest death toll worldwide after the United States.