Former Deputy President Jacob Zuma has apologised to South Africans for not using a condom during sex.
Zuma's comments on HIV shocked Aids activists
This detail emerged during his trial on a rape charge, of which he was cleared on Monday. It caused shock in a country where 5m people are infected with HIV.
Mr Zuma also said media coverage of his trial was unfair, and hinted at a political conspiracy against him.
He said he was "ready to lead" if his party wished. Mr Zuma was once seen as a future president and remains popular.
In a statement delivered to a news conference in Johannesburg, Mr Zuma said he had erred in having unprotected sex with a woman he knew to be HIV-positive.
"I should have known better and acted with more caution. For this I apologise to all the people of this country."
He also said he would continue to support the campaign against HIV/Aids and violence against women.
Mr Zuma said the woman who accused him "should in no way be vilified or condemned", and offered a hand of friendship "to the women and organisations who demonstrated against me, because we are partners in a common struggle".
He criticised the media coverage of his trial: "It is unfortunate that freedom of expression has been used as an instrument to assassinate character and prejudice the judicial process."
'Ready to lead'
Responding to journalists' questions about who he believed was responsible for charges being brought against him, Mr Zuma responded: "The campaign has been carried out at times by people without faces and I don't want to name names about who is behind this".
He later added: "I've often mentioned one person, [former chief prosecutor] Bulelani Ngcuka, who called some of your [journalist] colleagues to an off-the-record briefing to enlist him in his campaign against me."
Asked whether President Thabo Mbeki had been behind moves to prosecute him, Mr Zuma replied: "No, I have never said anything in that direction. I haven't seen his hand, and that's not something I'd want to discuss."
Asked if he would resume his duties in the structures of the governing ANC party - from which he was suspended when charged with rape last year - Mr Zuma said he was "ready to lead" if the ANC so decided.
Mr Zuma remained composed as he answered journalists' questions.
But he became visibly upset when a journalist challenged him on his admission made in court and widely reported in the media, that he had showered after sex to reduce the risk of HIV infection.
"If you've been in the kitchen, my dear, peeling onions, you wash your hands afterwards," he said.
Mr Zuma still faces a separate charge of corruption - which he denies - to be heard in July.
Analysts say evidence aired in the rape trial has badly damaged his reputation.
The BBC's Peter Biles say there is still uncertainty about his wider political future, with many observers questioning Mr Zuma's suitability to be a presidential candidate in three years' time.
Delivering judgement on Monday, Judge Willem van der Merwe said the state had not proved the rape case beyond reasonable doubt.
He also referred to evidence given by the defence, suggesting that the complainant had a history of making false accusations of rape.
Mr Zuma, who played a key role in the fight against apartheid, admitted having had sex with the woman, but insisted it was consensual.
Referring to their contradictory versions of the events of the night of 2 November 2005, the judge declared "the probabilities favour the accused's version".