The heads of Brazil's army, navy and air force have all resigned as President Jair Bolsonaro struggles to contain a crisis over his leadership, reports BBC.
The defence chiefs are reported to have stepped down in protest at what they see as an attempt by Mr Bolsonaro to exert undue control over the military.
On Monday, the president was forced to reshuffle his cabinet after his foreign and defence ministers both quit.
Mr Bolsonaro's popularity has plummeted over his response to Covid-19.
Brazil's far-right president, who came to power two years ago, has consistently opposed quarantine measures, arguing that the damage to the economy would be worse than the effects of the coronavirus itself.
He has also told Brazilians to "stop whining" about the situation. Nearly 314,000 people have died of Covid-19 in Brazil, with more than 12.5 million confirmed cases.
How serious is this for Bolsonaro?
It is reportedly the first time in Brazilian history that the chiefs of the army, navy and air force have stood down together over a disagreement with the president.
The three men - Gen Edson Leal Pujol, Adm Ilques Barbosa and Lt Brig Antonio Carlos Bermudez - resigned on Tuesday, a day after the president's loyal Foreign Minister Ernesto Araújo was forced to quit following heavy criticism by lawmakers.
Mr Araújo was accused of poorly handling relations with China, India and the US, which lawmakers said resulted in Brazil having insufficient quantities of Covid-19 vaccine.
Defence Minister Fernando Azevedo e Silva then quickly followed suit, prompting a cabinet reshuffle. The defence minister clashed with Mr Bolsonaro over loyalty of the armed forces, which he said should be directed to upholding the constitution rather than supporting the president personally.
The BBC's Latin America correspondent, Will Grant, says Mr Bolsonaro is now facing his biggest political crisis since taking office in January 2019.
Combined with his mismanagement of the coronavirus pandemic, our correspondent adds, the pressure on the right-wing leader has ramped up significantly in recent weeks.
Mr Bolsonaro, who has previously raised doubts about vaccines and defended unproven drugs as treatment, said last week that he would make 2021 the year of vaccinations. "Very soon we'll resume our normal lives," he said.
Brazil has been struggling with the rollout of its vaccination programme across the vast country. So far, it has been using the Oxford-AstraZeneca vaccine and China's CoronaVac, both of which require two jabs.
Brazil has also approved the use of the Pfizer/BioNTech vaccine and placed orders for the single dose Johnson & Johnson vaccine and the Russian-made Sputnik V jab.
Brazil's daily Covid-19 death toll passed 3,000 for the first time earlier this month, pushing hospitals close to collapse and raising fears that the country could become a threat to global public health.