The trial of former Brazilian president Jair Bolsonaro on charges of planning a coup d'etat opens Monday as the nation's Supreme Court hears from key witnesses, with the politician potentially facing decades in prison.

More than 80 people -- including high-ranking military officers, former government ministers and police and intelligence officials -- are to testify in a preliminary trial phase expected to last at least two weeks.

Bolsonaro could face up to 40 years in prison if convicted of plotting to remain in office after rival Luiz Inacio Lula da Silva had narrowly defeated him in October 2022 elections.

Prosecutors say he led a "criminal organisation" planning to declare a state of emergency so new elections could be held.

He also stands accused of being aware of a plot to assassinate Lula, his vice president Geraldo Alckmin, and Supreme Court Justice Alexandre de Moraes -- a Bolsonaro foe and one of the judges hearing the current case.

Bolsonaro has always denied any role in a coup attempt, blaming the charges on "political persecution."

Last week he told the Uol site that prosecutors were fabricating a "telenovela scenario," a reference to the melodramatic TV soap operas popular in Latin America.

'Death penalty'

The former army captain will be tried along with seven former aides accused of key roles in the alleged plot.

They include four former ministers, one former navy commander and the head of intelligence services during Bolsonaro's 2019-2022 presidency.

Several former Brazilian presidents have had legal entanglements since the end of the 1964-1985 military dictatorship, but Bolsonaro is the first to face coup charges.

A 900-page report by the federal police lays out the alleged coup plan in detail, saying it called for a decree ordering a new election -- and for Lula's assassination.

But the attempt failed to draw crucial military support and ultimately collapsed, prosecutors say.

The charges cover the riots of January 8, 2023, when thousands of Bolsonaro supporters invaded and sacked key government buildings, demanding a "military intervention" to oust Lula a week after his inauguration.

Bolsonaro was in the United States that day, but is suspected of having been behind the riots, which prosecutors say were the coup plotters' "last hope."

Despite his ban on running in elections, Bolsonaro has insisted he plans to be a candidate in next year's vote.

But after recent abdominal surgery -- his latest of many rounds to repair persistent damage from a knife attack in 2018 -- he has also said that a conviction now would be a "death penalty, political and physical."

Key figures will be questioned via videoconference during the preliminary trial phase beginning Monday led by de Moraes, who Bolsonaro supporters see as Enemy Number One.

The hearings are to begin at 3:00 pm local time (1800 GMT) Monday.