BBC News Online looks at what is known about the alleged mercenaries being held in Zimbabwe and Equatorial Guinea.
There are still few confirmed details about the men held
Zimbabwe's Home Affairs Minister Kembo Mohadi has said that all 64 men detained after their plane was impounded in Harare were African.
Zimbabwe state television described them as mostly white, "heavily-built males".
According to Mr Mohadi, Simon Witherspoon - referred to as a "known South African mercenary" - was the leader of the group.
He is reported to be a former member of the South African Defence Force, who joined the now defunct mercenary company Executive Outcomes (EO) in 1989.
'MERCENARIES' HELD IN ZIMBABWE
20 South Africans
One Zimbabwean with a SA passport
The minister said that Mr Witherspoon had operated in various countries in Africa including the Ivory Coast.
Another EO member - former British SAS officer, Simon Mann - has been named as a "co-conspirator".
He is said to have met the plane at Harare International Airport.
Details about the rest of the group are sketchy.
Angolan and South African diplomatic sources have said the suspects in Harare could be former members of the disbanded South African army unit, the "32 Buffalo Battalion".
"All that we know is that these the Angolans among the alleged
mercenaries belonged to the former Buffalo Battalion," Angolan Foreign Affairs Minister Joao Miranda said.
The "Buffalo Battalion" operated during the apartheid era and was made up of foreign soldiers, many of them from Portuguese-speaking countries.
The unit fought in Namibia and Angola in the 1970s and 1980s.
Of the 15 suspected mercenaries held in Equatorial Guinea, Nick du Toit has been presented as the group's leader.
He appeared on Equatorial Guinea state television saying that the men had been part of a plot to remove President Teodoro Obiang Nguema and put an exiled opposition leader in power.
Mr Du Toit - identified on television as a 48-year-old South African - is reportedly a former member of a South African reconnaissance unit.
He is also said to have links with Executive Outcomes.
EO was initially based in South Africa. In the 1990s, it was paid by the Angolan state oil company, Sonangol, to assist the Angolan army in regaining control of the Soyo oilfields from Unita rebels.
It was later involved in supporting the Sierra Leone Government in its attempts to defeat rebels.
The company closed when South Africa introduced its Regulation of Foreign Military Assistance Act - which prohibits the involvement of South Africans in mercenary activities abroad without due authorisation - in 1999.
But a South African security analyst told The Star newspaper that the three former EO members working together suggests that the company could be operating again.
Little is known about the rest of the group, other than South Africans are believed to be among them.
The incident has caused much embarrassment for the South African government.
The Foreign Ministry has said any of its citizens involved in mercenary activities are in "serious breach" of the Foreign Military Assistance Act.
It is disturbing to hear that "every time" the world dealt with mercenaries, South Africans were among them, Foreign Minister Nkosazana Dlamini-Zuma said.
"We definitely do not like the idea that SA is a pool for mercenaries."