The former head of a military research laboratory, Daan Goosen, told the commission that the project had the backing of South Africa's then Surgeon General, who described it as "the most important project in the country."

Although the substance was never developed, Mr Goosen said that an unknown European scientist claimed to have developed a strain of bacteria in the early 1980s "capable of killing pigmented people".

"It could have been used as a negotiation back-up," Mr Goosen told the Commission. "A thing like this could have been used to maintain peace. It was a case of being the strongest."

Plans to travel to Europe for a meeting were abandoned because of fears that it could be a trap, but the witness said South African scientists continued their own work on the project, and also looked into methods of making blacks selectively infertile.

Wouter Basson discussed killing Mandela

Goosen also said he and his immediate supervisor, Wouter Basson, had discussed the possibility of killing Nelson Madela and Oliver Tambo - then President of the ANC - through the use of carcinogens, as well as arranging the supply of snake venom "to eliminate an enemy of the state."

In other testimony, the former head of the police forensics laboratory, General Lothar Neethling, told the Commission that he had been instructed to supply Basson with confiscated supplies of narcotic drugs such as marijuana, LSD and Mandrax.

The intention, he said, was to extract the active ingredients for insertion into crowd-control grenades.

On Wednesday it was alleged that officials plotted to mentally disable Nelson Mandela with poison during the final years of his imprisonment

Mr Goosen told the commission he now realised that he was wrong to work on the projects, but said he had not been thinking rationally at the time.