Ranjeni Munusamy, a journalist for the Sunday Times was behind initial media reports that the ruling African National Congress (ANC) had once investigated Director of Public Prosecutions Bulelani Ngcuka on suspicion of acting as an agent for the apartheid government in the 1980s.

The allegations, which shook the ANC, emerged as Ngcuka's FBI-style Scorpions unit probed media charges that Deputy President Jacob Zuma had asked a French arms firm for a bribe in a big arms' deal.

Prosecutors said they had evidence against Zuma, but a case would be unwinnable, prompting him to rebuke Ngcuka for speaking out even though no charges were brought. Zuma has been invited to testify to the spy hearing.

The in-fighting is doing little for the ANC's credibility before general elections next year. Although it has no major opposition and is expected to stay in power easily, the party has battled perceptions of corruption and backroom dealing.

Violate press freedom

President Thabo Mbeki has ordered retired judge Joos Hefer to report to him on whether Ngcuka had indeed spied for the white apartheid government, and whether he and Justice Minister Penuell Maduna had abused their powers of public prosecution.

Hefer subpoenaed Munusamy, but her lawyers and media representatives said making her testify would violate press freedom and might put her in danger.

"Certain sources swore me to secrecy and told me that I would not be physically safe if I did (identify them)," Munusamy told the court in an affidavit on Thursday sources had called her cellphone, warning her not to name names. "On each occasion, they reminded me of my obligation and their threat."

Munusamy's editor at the Sunday Times refused to publish the story, so she passed on the information to a reporter at another paper, City Press, who broke the story.

Hefer, who opened his inquiry on Wednesday, ordered Munusamy to testify, but said she would be allowed to object to specific questions, suggesting she would not have to name her sources.

However, he allowed her legal team to appeal his ruling, which could take weeks. Hefer then postponed the hearings until 22  October, ensuring a slow start to an inquiry that has yet to hear evidence on Ngcuka.

It is the latest probe of top ANC figures after this year's fraud convictions of leading parliamentarian Tony Yengeni and Winnie Mandela, ex-wife of anti-apartheid icon Nelson Mandela.