Cape Town - The United Democratic Movement has joined the Democratic Alliance in calling for deputy president Jacob Zuma to step down.

"President (Thabo) Mbeki should protect the dignity of the presidency by asking Mr Zuma to step down," UDM leader Bantu Holomisa said on Monday.

He said there was an emerging consensus Zuma had not been cleared.

Public prosecutions head Bulelani Ngcuka announced on Saturday that Zuma would not be prosecuted over South Africa's multi-billion rand arms deal, despite indications that there may be a corruption case for him to answer to.

Allegations, which the deputy president has repeatedly rejected, are that Zuma tried to solicit a R500 000 bribe from Alain Thetard, the former Southern African head of French arms company Thomson CSF.

Holomisa said on Monday that Mbeki should "understand that we are not only dealing here with criminal evidence and the question of reasonable doubt.

"We are also dealing with a balance of probabilities and, party politics aside, the important thing is that damage is being done to the presidency and the country as a whole.

"He need not therefore wait for a conviction to ask the deputy president to step down to protect the national interest," he said.

On Sunday, DA Chief Whip Douglas Gibson said Zuma should resign in order to protect the dignity of his office, and "before there are further humiliations".

With acknowledgements to Sapa and News24.