One of President Thabo Mbeki’s main allies launched a sharp attack on the integrity of Jacob Zuma, deputy president of South Africa’s African National Congress, on Friday in a last-ditch attempt to slow his charge towards victory in the race for the party’s leadership.

Mosiuoa Lekota, the defence minister, said in the wake of Mr Zuma’s trouncing of Mr Mbeki in a key preliminary vote last weekend that the president’s camp had decided the “truth must come out” about Mr Zuma.