Hillary Clinton signs a new deal supporting efforts to fight AIDS in South Africa.
"South Africa and the entire region has a brighter and healthier and more secure future," she said while visiting a clinic in the Cape Town township of Delft.
"Even as we take a moment to say 'well done', we cannot make the mistake of thinking that our job is done," she said. "The disease is still very dangerous."
The United States has spent $3.2 billion since 2004 supporting South Africa's fight against AIDS. The new five-year agreement gives South Africa's government more control over the spending.
"Some people may hear 'South Africa is in the lead' and think that it means that the US is bowing out," Clinton said. "Let me say this clearly: the US is not going anywhere."
"The partnership is changing for the better," she said. "Our goal is no new patients -- zero."
The agreement highlights South Africa's shift from an international pariah on AIDS, under former president Thabo Mbeki, who refused to believe the scientific evidence that AIDS is caused by a virus -- to a celebrated one.
Now the country runs the world's largest AIDS treatment programme, with more than 1.3 million people receiving drugs, out of a total infected population of 5.6 million.
The rate of newborns catching the disease from their mothers during childbirth has fallen from 8 percent in 2008 to 2.7 percent last year.