The United Nations special envoy for Aids in Africa has closed a major conference on the disease with a sharp critique of South Africa's government.
South Africa's government refuses to fully endorse anti-retrovirals
Speaking at the end of the week-long gathering in Toronto, Canada, Stephen Lewis said South Africa promoted a "lunatic fringe" attitude to HIV/Aids.
Mr Lewis described the government as "obtuse, dilatory and negligent about rolling out treatment".
A South African delegate reportedly hit back over Mr Lewis' comments.
Health ministry official Sibani Mngadi told the AFP news agency that Mr Lewis had a "vendetta" against South Africa.
Earlier another keynote speaker said South Africa's health minister should resign because she had minimised the role of anti-retroviral drugs.
Manto Tshabalala-Msimang has strongly defended her approach to fighting HIV and Aids, saying that building up the immune system is of critical importance.
She said this week she wanted to give citizens choices, including traditional treatments like garlic, lemons and beetroots, instead of championing anti-retroviral drugs.
South Africa's governing ANC party has said the government approach to the disease was "responsible and integrated".
The International Aids Conference began in Toronto earlier this week with high hopes.
Microsoft founder and philanthropist Bill Gates made the opening remarks, and spoke optimistically of the potential of male circumcision and microbicides to reduce levels of HIV infection.
Hours before Mr Lewis spoke on Friday, 44 activists from South Africa's main Aids lobby group were arrested while protesting against Ms Tshabalala-Msimang's policies.
The lobby group, the Treatment Action Campaign (TAC), had said it would announce plans on Friday "to make sure the health minister is sacked tomorrow".
Mr Lewis, who says he is "persona non grata" in South Africa as a result of falling out with the health minister, criticised the arrest of the group's members.
"It really is distressing when the coercive apparatus of the state is brought against the most principled members of society," he said.
The BBC's Peter Greste, in Johannesburg, says Aids activists in South Africa will applaud Mr Lewis' comments.
He pulled few punches in a speech that drew loud cheers from the Toronto audience.
South Africa's Aids policy is "more worthy of a lunatic fringe than of a concerned and compassionate state," he said.
Tshabalala-Msimang has provoked fierce opposition at home
He derided the government's policies as "wrong, immoral [and] indefensible".
Up to 800 people a day die of Aids in South Africa, Mr Lewis said.
"The government has a lot to atone for. I'm of the opinion that they can never achieve redemption."
Mr Lewis also reserved some scorn for the G8 group of leading industrialised nations, who he said were undermining their own promises made at Gleneagles in 2005 to fight Aids, TB and malaria in Africa.
Funds were running dangerously low, Mr Lewis said, accusing the G8 of a "Pavlovian betrayal" of poorer southern nations.