The court's decision could escalate tensions in Sierra Leone coming after the attempted coup and a contentious election in which President Julius Maada Bio was reelected for a second term in June 2023.
Tensions have been on the rise in the country that is still recovering from a 1991-2002 civil war in which more than 50,000 were killed.
The result of the election was rejected by the main opposition candidate, and questioned by international partners including the United States and the European Union.
Gunmen on November 26 attacked military barracks, a prison and other locations in Sierra Leone, freeing about 2,200 inmates and killing more than 20 people.
The government said later that it was a foiled coup led mostly by Koroma's bodyguards. They summoned the ex-president for questioning at the start of December.
The former president condemned the attacks in a statement shortly after they happened.
Koroma's charges, which also include misprision of treason and two counts of harboring, were read out while he stood in the dock and some of his supporters cried in the courtroom.
"A dangerous precedent has been set ... We are dragging a former head of state — democratically elected — on trumped up charges under a political vendetta," Koroma’s lawyer, Joseph Kamara, told Reuters.
A high court later on Wednesday granted bail to the former president, who is currently restricted at his home in the capital. The case was adjourned until January 17.
According to Sierra Leone's penal code, a person found guilty of treason could face imprisonment for life.
Twelve other people have also been charged with treason in connection with the failed coup, including ex-police and correctional officers and a member of Koromoa's security detail, the government said on Tuesday.
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