United Nations General Secretary Kofi Annan has criticised the lack of progress in combating HIV.
Africa is worst hit by HIV
He said the vast majority of countries had fallen "distressingly" short of meeting their targets.
The general secretary was speaking at the opening of UN special conference in New York on how best to tackle the global HIV pandemic.
The meeting is one of the biggest since the UN General Assembly set out goals for tackling the virus in 2001.
The meeting will discuss how best to achieve a commitment made at last year's G8 Summit to give access to HIV drugs to all who need them by 2010.
Mr Annan said progress made in starting to reverse the HIV epidemic, but he warned that enormous problems remained.
He said: "The world has been unconscionably slow in meeting one of the most vital aspects of the struggle: measures to fight the spread of Aids among women and girls.
"These shortcomings are deadly."
Next week marks the 25th anniversary of the first documented case of Aids.
A report by UNAids released on Tuesday estimated that 38.6m people are living with HIV worldwide.
India now has the largest number of people infected with HIV, but the worst hit region remains sub-Saharan Africa.
In total 180 governments will be represented at the three-day conference.
The first two days will be given over to speakers from across the world who are working on the front-line to try to limit the spread of the virus.
The conference will end with a political declaration on the best way forward.
Dr Peter Piot, the head of UNAids, told delegates that Aids was one of the "make or break issues of our century."
Failure to properly address the pandemic would have catastrophic consequences, he said.
"It can only be defeated with sustained attention and the kind of 'anything it takes' resolve that member states apply to preventing global financial meltdowns or wars."
Dr Piot said annual funding would have to top US$20bn by 2008 if headway was to be made towards universal access.
Simon Wright, head of the HIV and Aids campaign run by the UK charity Action Aid, said world leaders had yet to demonstrate they were serious about universal access to drugs and treatment.
He said: "This is a massive undertaking and cannot afford another five years of missed opportunities."
Nick Partridge, chief executive of UK HIV charity Terrence Higgins Trust, said there was still much to do.
"Last year, three million people died with Aids. And for every five people in the developing world who need HIV drugs, only one person gets them.
"We need widespread prevention programmes and a greater commitment from governments and pharmaceutical companies to making anti-retroviral drugs widely available. Without this we're fighting a losing battle."