A South African judge presiding over the corruption trial of former President Jacob Zuma has withdrawn from the case - in a move likely to cause further delays.

Judge Piet Koen said he wanted to avoid any risk of compromising the perception of justice after he earlier ruled against Mr Zuma's efforts to force out the prosecutor.

Mr Zuma is facing 16 counts of fraud and racketeering over the purchase of fighter jets and other arms equipment when he was vice-president in the 1990s.

Eighteen months ago, Mr Zuma was given a 15-month jail term for contempt of court in connection with another corruption case.

He has denied any wrongdoing.