The jailed ex-president of Brazil, Jair Bolsonaro, has undergone a successful surgery for a double hernia, his wife Michelle says.

The former leader is serving a 27-year sentence for plotting a coup after he lost the 2022 presidential election to his left-wing rival, Luiz Inácio Lula da Silva.

Brazil's Supreme Court granted permission for the 70-year-old to be transferred from the room in the federal police headquarters where he is serving his sentence to a hospital in the capital, Brasília, for the procedure.

Ahead of the surgery, Jair Bolsonaro endorsed the candidacy of his eldest son, Flávio, for the 2026 presidential race.

The former president made his decision known in handwritten letter that was read out by Flávio Bolsonaro outside the hospital were his father is being treated.

"During my life, I have fought tough battles, paying a high price with both my health and my family, to defend what I think is best for our country," Bolsonaro wrote.

"I hand over what is most important in the life of a father - my own son for the mission of rescuing our country, Brazil."

Flávio Bolsonaro, a 44-year-old senator, had already announced his decision to run for president for his father's Liberal Party.

Ealier this month, he said his father had entrusted him "with the mission of continuing our national project". But Jair Bolsonaro's letter, which has been published by Brazilian media, is confirmation the senator has his father's backing.

The incumbent, President Lula, has already announced he plans to run again in the presidential election scheduled for October 2026.

In 2022, the presidential election went into a run-off, which saw the older Bolsonaro take on ex-President Lula.

When Lula narrowly won, Jair Bolsonaro refused to accept the result and plotted with top military leaders to prevent Lula from taking up office.

While the plot failed to enlist enough support from the military to go ahead, it did culminate in the storming of government buildings by Bolsonaro's supporters on 8 January 2023.

Bolsonaro was found guilty of coup-plotting and sentenced in September this year.

Despite the guilty verdict, the older Bolsonaro still wields considerable political influence.

Brazil's Congress passed a bill last week to significantly shorten Bolsonaro's sentence but President Lula said he would veto it.

Jair Bolsonaro is expected to be transferred back to federal police headquarters as soon as doctors give the go-ahead.