On Wednesday, the former Law and Order Minister, Adriaan Vlok testified under oath that while in office Mr de Klerk knew of illegal operations by the security forces against black opposition groups.

Mr Vlok and more than 30 senior police officers are seeking amnesty from the commission for a bombing campaign carried out during the 1980s.

Mr Vlok: testimony contradicts that of his former boss

In two earlier submissions to the commission, Mr de Klerk categorically denied that he knew of any illegal operations by his government.

The BBC southern Africa correspondent says the clear contradictions in the two men's accounts undermine the commission's integrity, but also show a measure of its success in getting to the truth - if rather late in the day.

All of the commission's 15 members have been summoned under the leadership of Archbishop Desmond Tutu to decide what they can do about Mr de Klerk.

The Deputy Chairman of the commission, Dr Alex Boraine, told the BBC the matter was very serious.

He said that two courses of action were being considered: calling Mr de Klerk before the amnesty hearing currently in progress or ordering a special session so that he can explain himself.

In his testimony, Mr Vlok also accused Mr de Klerk's predecessor PW Botha of ordering the bombing of the South African Council of Churches in 1988.