A leading American lawyer is planning to file a class action lawsuit against Switzerland's two biggest banks and US bank Citibank on behalf of victims of South Africa's former apartheid regime.

Ed Fagan, who played a key role in securing compensation for Holocaust survivors from Swiss banks, told the French news agency AFP he would begin proceedings at a New York court on Monday.

He declined to specify the amount being sought, but Swiss newspaper SonntagsZeitung said UBS and Credit Suisse face demands for 80bn Swiss francs ($51.3bn; 60bn euros).

The banks are accused of profiting from loans to the white South African government while a United Nations embargo was in force.

The banks say they have no knowledge of a lawsuit, but a Credit Suisse spokeswoman said that to blame them for the injustices of apartheid would be preposterous and unsubstantiated by the facts.

Complicated case

The case will be coordinated by South African human rights lawyer Dumisa Ntsebeza.

"The regime would never have survived so long if it had not gone on being supported ... by firms whose only goal was profit," SonntagsZeitung quoted Mr Ntsebeza as saying.

The case is being pursued in the American courts under laws permitting non-US citizens to file human rights claims against companies doing business in the United States.

But the suit is likely to be complicated by jurisdictional issues.

Switzerland did not take part in a United Nations-led round of trade sanctions against South Africa, although it did observe an arms embargo.

In 1998, a group of Swiss banks agreed to pay $1.25bn to settle legal action arising from the alleged hoarding of holocaust victims' bank accounts after World War II.