The leaders of all three branches of Brazil’s armed forces jointly resigned on Tuesday following President Jair Bolsonaro’s replacement of the defence minister.

The switch of ministers has fuelled widespread apprehension of a military shake-up to serve the president’s political interests.

The Defence Ministry reported the resignations — apparently unprecedented since at least the end of military rule 36 years ago — in a statement released without giving reasons.

Replacements were not named, but analysts expressed fears the president, increasingly under pressure, was moving to assert greater control over the military.

“Since 1985, we haven’t had news of such clear intervention of the president with regard to the armed forces,” said Carlos Melo, a political science professor at Insper University in Sao Paulo.

Mr Bolsonaro a conservative former army captain who has often praised Brazil’s former period of military dictatorship, has relied heavily on current and former soldiers to staff key Cabinet positions since taking office in January 2019.

Mr Melo said the military itself had so far refrained from politics, but added: “Will this resistance continue? That’s the question.”

The announcement came after the heads of the army, navy and air force met with the new defence minister, General Walter Souza Braga Netto, on Tuesday morning.

A retired army general who has a relationship with the three commanders as well as with Mr Braga Netto, told The Associated Press on condition of anonymity: “there was an embarrassing circumstance so they all resigned”.

Mr Bolsonaro on Monday carried out a shake-up of top Cabinet positions that was initially seen as a response to demands for a course correction by politicians, diplomats and economists, particularly over his handling of the pandemic that has caused more than 300,000 deaths in Brazil

That included the replacement of Defence Minister Fernando Azevedo e Silva, who said in his resignation letter he had “preserved the armed forces as state institutions”, a nod to his efforts to keep generals out of politics.

Mr Bolsonaro has often bristled at the checks and balances imposed by other branches of government and has attended protests targeting the Supreme Court and Congress.

He has also criticised the Supreme Court for upholding local governments’ rights to adopt pandemic restrictions that he adamantly opposes, arguing that the economic effects are worse than the disease itself.

His recent slide in popularity, and the sudden likelihood that he will face leftist former President Luiz Inácio Lula da Silva in the 2022 presidential election, has analysts saying he is looking to the armed forces for support.

Retired Gen. Carlos Alberto Santos Cruz, who previously served as Bolsonaro’s government secretary, appeared to refer to such concerns when he responded to early rumours of military resignations with a tweet saying: “The armed forces won’t go on an adventure.”