Britain must take a lead in trying to ensure greater access to HIV drugs in the developing world, the UN says.
Africa is the centre of the epidemic
Stephen Lewis, special envoy to the UN Secretary General, launches his Stop Aids campaign in London on Tuesday.
He is calling for Tony Blair to use Britain's upcoming presidency of the G8 group of rich nations to lobby for more funds for treatment in Africa.
Lack of resources threatens the World Health Organisation's target of 3m people in treatment by the end of 2005.
Mr Lewis told BBC Radio 4's Today programme: "The international community has been focusing on prevention for years.
"What we have not done yet is provide treatment, give people hope and encourage them to get tested.
"This is what generates a sense of prevention. The two go together inseparably.
"The G8, if it puts its minds to it, can provide the resources and the assistance to make the target of 3m by the end of 2005 real."
Mr Lewis said there was a real momentum towards providing treatment in Africa - the epicentre of the global HIV pandemic.
But he said the good work was threatened by a lack of money.
Mr Lewis said: "If they can maintain the resources, then these countries are going to break through and the whole world will finally have a sense that we can turn this
Mr Lewis said only a tiny fraction of the money spent on war and reconstruction in Iraq and Afghanistan had been devoted to HIV.
"We have to bring an end to that at some point," he said.
"This is a government in this country that can do that, perhaps more effectively and with greater conscience than can others, because they are involved in both sides of the equation.
"If Tony Blair wants to turn the G8 on its head, he can do so. It didn't happen in Canada. It didn't happen in Japan. It can presumably happen in the UK."