UN Secretary-General Kofi Annan has said in an interview that AIDS is a "weapon of mass destruction" for some countries and the world is losing the fight against the epidemic.
He urged world leaders to do more to stem the spread of the disease.
"In some of the countries we are talking about, AIDS is a real weapon of mass destruction - and what are we doing about that?" Mr Annan said in the interview with BBC World Service radio.
"It does indicate a certain incredible callousness that one would not have expected in the 21st century."
The United Nations said in a report this week that deaths and new cases of HIV/AIDS reached unprecedented highs in 2003 and were set to keep rising. About five million people were infected in 2003 and more than three million died.
It said new global estimates showed about 40 million people worldwide were now living with HIV/AIDS.
"I am not winning the war because I don't think the leaders of the world are engaged enough," Mr Annan said in excerpts of the interview released to the BBC's website. "I feel angry, I feel distressed, I feel helpless . . . to live in a world where we have the means . . . to be able to help all these patients, what is lacking is the political will."
Sub-Saharan Africa was the worst affected region, according to the UN figures, with about 3.2 million new infections and 2.3 million deaths in 2003.
The report said the epidemic was fuelled by intravenous drug use and unsafe sex. It is spreading in India, China, Indonesia, Papua New Guinea, Vietnam, the Russian Federation, Ukraine, Estonia and Latvia.
Mr Annan's interview was due to be broadcast at 3:30 a.m. on Saturday.