President Jacob Zuma had undermined the struggle against HIV/Aids by having unprotected sex again, the Democratic Alliance (DA) said on Sunday.

This, after the Sunday Times reported that he fathered a love-child with the daughter of soccer boss Irvin Khoza.

"President Jacob Zuma's behaviour directly contradicts the government's campaign against multiple sexual partners, and the inherent HIV/Aids risk in having unprotected sex," said DA leader Helen Zille in a statement.

All the President's men were mum about the baby girl, reportedly born to Sonono Khoza, 39, on October 8 last year.

The Sunday Times reported that the child, Thandekile Matina, was given Zuma's surname and was registered as his daughter. He now has 20 children.

Zuma's behaviour was "in stark contrast" to the government's efforts to promote safe sex through condom use, especially in the case of multiple sexual partners, Zille said.

She likened Zuma's behaviour to that of former President Thabo Mbeki, whose denialist stance on HIV/Aids was found, by a Harvard University to have possibly contributed to the deaths of more than 300 000 South Africans during his tenure.

"South Africa now has a President who, both through his words and actions, is doing similar damage to the struggle (against HIV/Aids) - a life and death struggle for millions of South Africans," Zille said.

In 2006, Zuma was acquitted of raping the HIV-infected daughter of a close family friend.

Judge Willem van der Merwe found that Zuma had consensual sex with her.

"I wish to state categorically and place on record that I erred in having unprotected sex. I should have known better and I should have acted with greater caution and responsibility," Zuma said after his acquittal.

However, Zille said on Sunday that "that acknowledgement has faded from his memory, and he has once again succeeded in sending the wrong message to the South African people".

Zuma's spokesperson Zizi Kodwa could not immediately comment on the love-child claim on Sunday. Presidential spokesperson Vincent Magwenya could not be reached. Also not available telephonically was Irvin Khoza. His voicemail was full.

Khoza chairs Orlando Pirates and the World Cup Local Organising Committee and is vice-president of the South African Football Association.

He shared a stage with Zuma during his post-election celebration at his Nkandla homestead in KwaZulu-Natal in June 2009 and received an honorary doctorate in philosophy from the University of Zululand in 2004, when Zuma was its chancellor.

Quoting a "close family friend", the Sunday Times reported that a delegation from Zuma's family visited the Khoza family in December last year to discuss Zulu customary damages, called inhlawulo, payable when a child is born out of wedlock.

However, when Sonono was contacted for comment by the newspaper, she said: "I don't know what you are talking about. I definitely don't know what you are talking about," before ending the call.

Sonono is an events manager in the marketing division at Absa Bank's Johannesburg headquarters. She has two other children from a previous marriage.

According to the newspaper report, Zuma himself visited the Khoza home in Diepkloof on January 17, when he spent almost an hour with Sonono and the infant.

Irvin Khoza was not at either of the meetings, but was said to feel betrayed and humiliated about Zuma's relationship with his daughter. Khoza's youngest daughter, Zodwa, 30, died in 2006 of HIV/Aids-related causes. She had been the brand manager of Orlando Pirates.

Zuma, 67, wed his third wife Thobeka Madiba earlier this month, two years after his marriage to Nompumelelo Ntuli. He married Sizakele Khumalo in 1973. His first wife Kate Mantsho Zuma committed suicide in 2000 and he divorced Nkosazana Dlamini-Zuma, who is Home Affairs Minister, in 1998.

He is engaged to Gloria Bongi Ngema, from Durban, whose family presented umbondo (gifts) to the Zuma family at the end of December.

Zuma defended his polygamy and called for an acceptance of Zulu culture at the World Economic Forum in Davis, Switzerland, last week.

He said he believed in the "equality of women", and that he treated his wives equally.

Polygamy was part of his culture, and those who thought their culture was "superior" had a problem.

Zuma dismissed a suggestion that polygamy was "symbolically a great step backward" or inherently unfair to women.

"It depends what culture you come from. People interpret cultures in different ways. Some think that their culture is superior to others, that's a problem we have in the world."

South Africa followed a policy of respecting the cultures of others.

"That's my culture. It does not take anything from me, from my political beliefs and everything, including the belief on the equality of women.

"It's my culture. And I'm sure there are cultures (that) do that kind of thing," he said.

"The problem is that when people have their own culture ... think that their culture is the only right one... the only one accepted by God."