Ex-South African president Jacob Zuma's son Duduzane denied wrongdoing at a graft inquiry on Monday, dismissing the testimony of two witnesses who placed him in the room when friends of his father are alleged to have offered large bribes.

Duduzane Zuma is a key witness at the so-called "state capture" inquiry set up by presidential decree last year to test allegations of high-level corruption during Jacob Zuma's nine years in power.

The inquiry has shocked South Africans with revelations about the brazen way in which some people close to Jacob Zuma allegedly tried to plunder state resources and influence policymaking.

But the investigation has struggled to nail down convincing evidence of corruption involving top officials.

Duduzane Zuma was a business partner of the Guptas, three Indian-born brothers accused of using their friendship with the former president to win state contracts in the years leading up to Zuma's ousting as head of state in February 2018.

Former deputy finance minister Mcebisi Jonas told the inquiry last year that a Gupta brother offered him a 600-million-rand (40 million U.S. dollars) bribe and the position of finance minister at a meeting arranged by Duduzane in 2015, on the condition that Jonas would assist the Guptas with their business ventures.

Duduzane Zuma said on Monday that he did arrange a meeting involving Jonas at a Gupta residence in Johannesburg in 2015, but his testimony about the meeting differed on almost every other detail.

He said the meeting was between himself, Jonas and businessman Fana Hlongwane to discuss a rumor that Hlongwane was blackmailing Jonas and that the gathering had not ended acrimoniously, as Jonas had reported.

"After the meeting, everything was cool," said Duduzane Zuma. "As I've mentioned in my affidavit, I've bumped into Mr Jonas once or twice subsequent to that meeting, and my view was there was no hostility."

He said he had held similar informal meetings at the Gupta residence "all the time."

Asked about testimony by an ex-provincial official that he was present at another meeting at the Gupta house where a large bribe was allegedly offered, Duduzane Zuma denied he was present.

He said he had been "conveniently placed at the crime scene most times" and suggested that the testimony of a third witness was a waste of paper.

The Guptas, who left South Africa shortly after Jacob Zuma's removal, have not appeared before the inquiry but have submitted an affidavit in which they denied allegations against them.