Sixty-four men said to be mercenaries planning a coup in Equatorial Guinea and three air crew are due to face charges in Zimbabwe within days.
Military equipment was reportedly found on the impounded plane
The group's plane was seized in Harare on Sunday. A government minister said the men could face the death penalty.
In Equatorial Guinea, a man said to be related to the group has publicly confessed to a coup plot on television.
On Thursday, Equatorial Guinea asked South Africa for help in the trial of another 15 suspected mercenaries.
The men - arrested in Equatorial Guinea - were reportedly involved in the same alleged plot.
South African President Thabo Mbeki said Equatorial Guinea wanted South African assistance to ensure the trial of the 15 men was transparent and fair.
"It was a direct request," Mr Mbeki said after meeting officials from the oil-rich state in western Africa.
Other reports say the 64 suspects who flew to Harare from South Africa were security guards bound for other states but who had stopped for mining supplies.
The company which chartered their plane said they had stopped in Harare en route to Burundi and DR Congo where they were due to provide security services for an internationally run mine.
But Zimbabwe and South Africa both support the government of Equatorial Guinea and say the men were part of a plot to overthrow the president, Teodoro Obiang Nguema.
Harare has accused the men of working for US, British and Spanish intelligence agencies.
The BBC's Alastair Leithead in South Africa describes the British and American links as spurious but adds there is growing evidence that the mystery does relate to a coup attempt gone wrong.
Attorney General Bharat Patel said the charges against the men were "still being worked out," but they said the group were likely to be charged with "contravening the Aviation Act".
He said there may also be other charges relating to offences under the firearms law and possibly the country's immigration laws.
Foreign Minister Stan Mudenge said on Wednesday the men could "face capital punishment". But the charges listed by the attorney general are not capital offences.
Mr Patel said the men were expected to appear in court on Friday or Saturday.
History of coups
The group of the 64 detained men consisted of about 20 South Africans, and also Angolans, Namibians, Congolese and one Zimbabwean national, South African Foreign Ministry spokesman Ronnie Mamoepa told the BBC's World Today programme.
Equatorial Guinea and its president have a long history of coups
"We are awaiting the outcome of investigations into this matter, and if indeed it leads to a trial, we will monitor the trial to see if it is fair," Mr Mamoepa said.
The president of Equatorial Guinea said early South Africa had warned him that a group of mercenaries was heading for his country and he suggested that they had had foreign backing of hostile foreign powers and multinational firms.
A man said to be the leader of the "mercenaries" has appeared on Equatorial Guinea state television to say that they had been part of a plot to remove Mr Obiang and put an exiled opposition leader in power.
"It wasn't a question of taking the life of the head of state but of spiriting him away, taking him to Spain and forcing him into exile and then of immediately installing the government-in-exile of Severo Moto Nsa," said the alleged coup leader, introduced as Nick du Toit, according to a transcript released by AFP news agency.
In Spain, Mr Moto, who led a failed coup bid in Equatorial Guinea in 1997, denied any role in the alleged plot but also launched a blistering attack on President Obiang, who himself took power in a coup in 1979.