Deputy President Jacob Zuma has become a political liability, both to the African National Congress and South Africa, and should step down, says Democratic Alliance leader Tony Leon.

In a speech delivered at noon on Thursday at the University of KwaZulu-Natal's Durban campus, he called on President Thabo Mbeki to ask his deputy to resign.

Leon said Mbeki should also extend the terms of reference of the Hefer Commission, appointed by the president to investigate allegations of spying made against National Director of Public Prosecutions head Bulelani Ngcuka.

The DA leader criticised recent robust exchanges between Zuma and Ngcuka, who have been at loggerheads since the Scorpions investigations unit announced it was investigating Zuma on bribery allegations related to the arms deal.

"The ANC has ceased to behave like a government at all. It is starting to behave like the Mafia. Its vendettas are now being fought out in public, and the bodies are piling up."

Mbeki has to ask Zuma to step down. "At least temporarily, in the event that the deputy president chooses to take legal action against the Scorpions to clear his name."

With acknowledgements to Sapa and The Natal Witness.