President Thabo Mbeki has rejected calls for Jacob Zuma to stand down and expressed his confidence in Bulelani Ngcuka.

Answering a question from Democratic Alliance leader Tony Leon in parliament, Mbeki yesterday poured scorn on the suggestion that Deputy President Zuma should be sacked until the corruption allegations against him are refuted.

Leon, who is on a visit to London, was not in parliament yesterday, but DA chairman Joe Seramane engaged Mbeki in follow-up questions.

Mbeki trod a fine line in the acrimonious stand-off between Zuma and National Director of Public Prosecutions Ngcuka. On one hand he insisted Zuma was entitled to the presumption of innocence until proven guilty, while on the other he expressed confidence in Ngcuka, Zuma's adversary.

Mbeki said while the allegations against Zuma were just that - allegations - he was "confident" Ngcuka would discharge his responsibilities as required in law. "I have not and will not question his decisions."

The president said no one could produce evidence about corruption in the arms acquisition package process, but he stopped short of saying he had the fullest confidence in his deputy.

In a sarcastic reference, Mbeki said he was interested to learn that for the "first time the leader of the official opposition is interested" in protecting the reputation of the government.

"His question suggests that we should, on the basis of allegations, reconstitute the government ... starting with the sacking of the DP (Zuma), even if this is on a temporary basis ...

"From this statement I presume he has made the determination that the allegations of corruption against the DP have had a significantly or decisively negative impact on the government and the country."

Mbeki said the DA should substantiate its allegations. He would not take disciplinary action or any other action "simply on the basis of allegations, whoever makes these allegations", he said.

"I must state this clearly and unequivocally that the president is not a court of law. Neither has anybody approached me to give me proof of any of the allegations that have been made about the deputy president and, indeed, the national director of public prosecutions."

Louis Green, vice-president of the African Christian Democratic Party, in his question to Mbeki, noted that Ngcuka had decided not to prosecute Zuma even though the National Prosecuting Authority had claimed they had prima facie evidence that Zuma was involved in arms deal corruption.

In terms of internal cabinet rules, which state that a member may not expose himself to conflict of interest, Mbeki could discipline Zuma on the basis of persuasive prima facie evidence, Green said.

He asked Mbeki whether he would use these measures to sanction Zuma. Mbeki appeared to evade the question and said Ngcuka had said he did not have evidence to secure a conviction.

He could therefore not understand why he was being asked to act against Zuma on the basis of this kind of evidence, Mbeki said.

Zuma started the day's proceedings with his usual jocularity.

He also chuckled when ANC members booed the DA and opposition questioners.

With acknowledgements to the Political Bureau and The Star.