South Sudan's detained former vice-president Riek Machar is "ready" to face trial and will appear in court on Monday, his lawyer told AFP on Saturday, as fears grow of renewed insecurity in Africa's youngest nation.

The government of President Salva Kiir this month charged Machar with murder, treason and crimes against humanity and stripped him of his position as first vice-president in the unity government.

His position was part of a 2018 deal between the two men that ended a five-year civil war that killed some 400,000, but the fragile agreement has been unravelling for months.

"The accused is ready for the trial. He is ready and he is in good health," his lawyer, Kur Lual Kur, told AFP.

He confirmed Machar would attend the "special court" for the first sitting on Monday following a summons, but said they were still waiting for details.

"We are ready for the trial, but up to now we didn't receive the formation of the court," he said.

"We will go according to that summons and then we will see what is going to happen on that day," he added.

Machar's faction has denied the charges -- which also include an accusation he ordered an ethnic militia to attack a military base this year -- and says they are part of Kiir's efforts to sideline the opposition and consolidate power.

South Sudan, which gained independence from Sudan in 2011, has remained mired in poverty and insecurity with repeated international attempts to ensure a democratic transition failing.

Elections due to have taken place in December 2024 were again postponed to 2026 and the two sides have not merged their armed forces.