Johannesburg - National Director of Public Prosecutions Bulelani Ngcuka has accused senior government and ANC figures being investigated by the Scorpions of waging a vicious campaign to discredit him and his department.

"There has been a systematic disinformation campaign to discredit me and my organisation by those whom we are investigating, thereby diverting public attention from their ... conduct," Ngcuka said.

"We have acted without fear, favour or prejudice in defence of democracy," said Ngcuka in an address to the annual dinner of the Foreign Correspondents Association (FCA) on Saturday night.

While he did not name Deputy President Jacob Zuma or ANC veteran Mac Maharaj, he left little doubt that his remarks were directed at them and others - like Zuma's financial adviser Schabir Shaik - under investigation by the Scorpions in their probe into corruption in the multi-billion-rand arms deal.

"Their strategy was simple: 'Throw as much dirt on them as you can, and hope that some of it sticks.'

"But this has failed and will continue to fail for it does not matter how deep the truth may be buried, it is never destroyed," he said.

Ngcuka hit back at his critics within the ruling African National Congress (ANC) and said he would be vindicated in his statement that there was prima facie evidence of corruption against Zuma.

"Evidence against the deputy president will come out in the trial of Shaik," he said in response to a question.

"Then you will see that there is prima facie evidence," Ngcuka said.

He said that when dealing with a head of state or deputy president you could not afford to lay charges unless you were assured of success.

He said his team in the Scorpions had taken a decision that they should prosecute.

"I found some shortcomings and they agreed that there were shortcomings which meant there was not sufficient evidence to guarantee a conviction."

He said it would have been wrong to lie to the public and would have compromised the institution if he had done so.

"I believe I made the right statement," Ngcuka said.

"The decision to investigate the deputy president was not an easy one."

In his speech to the FCA, Ngcuka said that although the Scorpions had had successes in the majority of high-profile cases, it was the investigation into the arms deal that had marked the biggest test for democracy in South Africa.

"I believe it is the commitment to our ideals and support for the safeguard and protection of our democracy that the NPA finds itself under attack."

He said the NPA had been able to conduct the investigation and take the decisions without any political interference or interventions.

"The decisions were not popular and clearly made some people uncomfortable," he said.

Ngcuka said that despite the unpopularity of the decisions, they had not resulted in a national calamity.

He praised the conduct of the media overall but said some journalists had abused their positions.

He did not name names but clearly most of his remarks were directed at former Sunday Times journalist Ranjeni Munusamy and City Press editor Vusi Mona who published allegations that Ngcuka was an apartheid spy after then Sunday Times editor Mathatha Tsedu had refused to do so.

Instead, and in breach of journalistic ethics, the journalist passed the story to a rival newspaper under circumstances in which a number of editors of different newspapers refused to publish the story.

Returning to Munusamy without naming her, Ngcuka said the journalist who had written "the series of articles and conducted radio interviews on various allegations against me" was now refusing to co-operate and convey the story to ... (the Hefer Commission) that has been established to get to the bottom of the issues.

"If it was in the public interest that the story be published at the time, surely it should also be in the public interest for the commission established to probe the allegations to expect co-operation of the journalist," Ngcuka said.

With acknowledgements to John Battersby and the Cape Times.