Sir Mark Thatcher has been included on a new list of nine suspects being linked to an alleged plot to overthrow the president of Equatorial Guinea.
Sir Mark faces a trial in his absence
The nation's attorney general, Jose Olo Obono, denied earlier reports that they would be tried in their absence.
Last month, Sir Mark appeared in court in Cape Town as his lawyers argued against an order forcing him to answer questions about a suspected coup plot.
Lady Thatcher's son denies knowledge of, or involvement in, any plot.
Mr Obono said Equatorial Guinea may try at a later stage to extradite all the people it is accusing of involvement.
The nine foreigners on the list are accused of helping to finance a plot.
The announcement came on Tuesday, as the trial of 19 defendants accused of seeking to overthrow the president of the small, oil-rich West African nation, Teodoro Obiang Nguema, resumed after a two-month recess.
South African Nick du Toit is accused of being in charge of logistics for an attempted coup against the president.
Mr du Toit, 48, who was the only defendant to have admitted to a minor role in a plot, retracted his confession before the court in Malabo on Tuesday.
He said: "There was no attempted coup d'etat in this country.
"I had to tell these people what they wanted. It was the only way to stay alive."
Mr Obono denied claims that Mr due Toit had been mistreated and said he had voluntarily given investigators vivid details of plans for an attempted coup.
In Equatorial Guinea, the state prosecutors have already charged 19 people, including eight South Africans - one of whom is Mr du Toit - a six-man Armenian air crew and five Equatorial Guineans, one of whom is a former deputy government minister.
Map of South Africa
They were alleged to be a reception committee for a group of mercenaries supposed to fly in from Zimbabwe and guide them to their targets in Equatorial Guinea.
The men accused of being involved - mainly South Africans - were arrested in Harare on 7 March.
Sir Mark, the son of former UK Prime Minister Margaret Thatcher, was arrested in August by South African police and released after posting bail of £167,000, reportedly paid by his 78-year-old mother.
He is accused of helping to fund the purchase of a helicopter, breaching laws banning South African residents from taking part in foreign military action.
His lawyers maintain the funds were an investment in an air ambulance venture for west Africa.
Sir Mark could face 15 years in jail if convicted. in South Africa.
In September former British SAS officer Simon Mann, suspected of leading the alleged mercenaries, was jailed for seven years in Zimbabwe for illegally trying to buy weapons.
Equatorial Guinea, a former Spanish colony, has been ruled by President Obiang since he seized power from his uncle in a coup in 1979.