Cyril Ramaphosa is facing allegations that he covered up the theft of a huge sum of money from his farm.

The controversy comes ahead of next month's ANC conference with the president seeking a second term in office.

Ms Sisulu - who says she wants the top job herself - told the BBC's Newshour programme that Mr Ramaphosa should step down, as he was holding the whole party to ransom.

Next week parliament is due to discuss the issue and the president, who denies any wrongdoing, could potentially face impeachment.