The world is losing the war against Aids, United Nations Secretary General Kofi Annan has warned.
Africa has been worst hit by Aids
In a BBC interview, Mr Annan criticised political leadership in the developed as well as the developing world.
He urged people in the developing world to challenge their own governments and insist on their right to support.
Forty million people are infected with the HIV virus that may lead to Aids - three million have already died of the disease this year alone.
Asked if he, as head of the UN, was winning the war against Aids, Mr Annan said: "I'm not winning the war because I don't think the leaders of the world are engaged enough."
Mr Annan said it was unjust that Aids was manageable in the rich world but a death sentence for people elsewhere.
He said the developed world - in particular the United States and the European Union - had failed to provide the resources needed to pay for anti-retroviral drugs, set up prevention and testing programmes, and train doctors and nurses.
"I feel angry, I feel distressed, I feel helpless... to live in a world where we have the means, we have the resources, to be able to help all these patients - what is lacking is the political will."
He said many governments had described Aids as a security problem, yet were not giving it the level of attention devoted to terrorism and weapons of mass destruction.
"For people in some of the countries we are talking about, Aids is a real weapon of mass destruction - and what are we doing about that?
"It does indicate a certain incredible callousness that one would not have expected in the 21st Century."
Mr Annan also criticised African leaders who, he said, were allowing their people to die because they were too embarrassed to talk about condoms.
"We had a situation where one African leader was going to give a speech... and a speech was prepared for him where he was urged to encourage the young people and the population to use condoms to protect themselves.
"He said: 'I can't utter the word condoms. I'm the father of the nation. You can't ask me to encourage the youth to be promiscuous.'
Many children are brought up by their grandparents as their parents die
"But this is saving lives."
Mr Annan said he was now "talking to people over the heads of the governments".
"They should take on this fight. They should not be afraid to speak up, and they should not be afraid to challenge their governments to do something about the epidemic.
"They have the right to demand action from leaders whose main and major responsibility after all is to ensure the safety and welfare of their people."
Mr Annan was interviewed by Carrie Gracie to mark the end of the BBC World Service Aids season.
You can listen to the interview from 0330 GMT on Saturday 29 November on the BBC World Service.