South Africa's former President Jacob Zuma has requested the head of a commission investigating corruption during his presidency to step aside over alleged "bias", his lawyers said.

Mr Zuma has repeatedly refused to testify at the commission.But Deputy Chief Justice Raymond Zondo has set a "non-negotiable" date for him to appear.Allegations of corruption dogged Mr Zuma's presidency and led him to resign in February 2018.

The former president's lawyer has said that he would not take part until Mr Zondo is replaced.

In a letter to the commission, Eric Mabuza said: "We are instructed to seek your recusal as chairperson of the commission on the ground that our client reasonably apprehends that you have already adopted a biased disposition towards him.

"He said that Mr Zondo was no longer capable of "exercising an independent and impartial mind".

'State capture'

"President Zuma has always expressed his willingness to cooperate with the commission. This is in spite of his reservations about the legality of the commission and in particular, your suitability as chairperson, given your personal relations with him".

The inquiry, known as the Zondo Commission, was established to investigate the "state capture" scandal during Mr Zuma's tenure as president.

This centred around allegations about an Indian business family, the Guptas, who won lucrative contracts with state companies.The family has also been accused of trying to influence political decisions, including the naming of ministers.

The Guptas have said that there were no cases to answer and that they were in the process of clearing their name "in the face of unfounded media allegations".

'Too ill'

Mr Zondo has chaired the commission for more than two years and it has heard testimony from ministers, ex-ministers, government officials, politicians and business executives.

Last week Mr Zuma said he was too ill to testify.As a result, Mr Zondo held a televised media briefing where he ordered Mr Zuma to testify in November.

Making a televised announcement "attests to the fact that he seeks to portray him as uncooperative and belligerent in the eyes of the public", Mr Zuma's lawyer argued in the letter.