The South African government is being sued, along with major corporations, by alleged victims of the apartheid era.
President Mbeki will fight the lawsuit, says his spokesman
The suit, filed in New York, seeks $10bn for "genocide, expropriation and other wrongful acts" by the firms under apartheid, said the US lawyer Ed Fagan.
Controversially, it also demands another $10bn from the post-apartheid government for "continuing to allow companies to exploit victims".
The government plans to defend itself, but would prefer it resolved in SA.
The lawsuit targets mining firms Anglo-American and Goldfields; US computer giant IBM; UBS Bank of Switzerland and local petroleum company Sasol.
"At the end of the day these companies were strategic partners of the (apartheid government)", Mr Fagan told a news conference.
He said President Thabo Mbeki's government was also being targeted "because of its failure to fulfil its obligations and its conspiracy with specific companies to violate these people's rights".
Mr Fagan said the action demanded that the government and the companies should pay a $20bn "humanitarian fund".
He said one of the plaintiffs in the action is Dorothy Molefi, the mother of 13-year-old activist Hector Petersen, who was shot dead in the Soweto riots in 1976.
Mr Fagan filed the action on behalf of alleged apartheid victims
Mr Mbeki's spokesman, Bheki Khumalo, said the government would defend itself.
"If Ed Fagan has decided to do this - and he has indicated that he is doing it - well, the government will have to go to court and defend itself. We are convinced that we have a winnable case," he said.
Mr Fagan said the civil action was separate to that of a class action on behalf of apartheid victims already before a New York court, where 34 companies are being sued for billions of dollars.