Christian Aid's head of policy Mark Curtis went further and said the new fund is simply "window-dressing".
Kofi Annan has urged countries and private organisations to contribute to the global Aids and health fund he launched last year.
The money raised is intended to fund a coordinated approach to fighting HIV/Aids, amongst other illnesses.
A recent report by the UN Programme on Aids and HIV (UNAids) said more than half the money ($4.63 bn) needs to be spent in Africa.
UNAids gave a breakdown of how the money should be spent. It suggested that $3.07bn should go on care and support of those with HIV and $1.56bn should be spent on prevention.
Mr Annan announced the establishment of the fund in April but so far just over half a billion dollars has been pledged. UNAids is saying that it does not expect to be able to use the full amount until 2005.
In recent months, there has been a lot of emphasis on the production of cheap generic anti-retroviral drugs to prolong the lives of those with HIV, but some argue that prevention should be the focus of an anti-Aids strategy.
Infrastructure needs
For example, the UK charity Christian Aid says the emphasis should be on building up the national and local health infrastructures in various countries.
Christian Aid's head of policy Mark Curtis went further and said the new fund is simply "window-dressing".
"There is a serious risk," he said, "that it will actually divert attention and money away from reducing the underlying poverty on which HIV/Aids thrives."
The medical charity Medicins Sans Frontieres (MSF) argues the opposite case. It is concerned that there is not enough emphasis on treatment.
Patients' needs
MSF notes that a draft declaration that delegates at the UN special session are expected to approve devotes more paragraphs to prevention that treatment, and that there is only one mention of anti-retroviral drugs.
"You cannot simply write off millions of people," said Dr Anne-Valerie Kaninda of MSF, "by saying the treatment is not available. Prevention alone will not solve the problem."
The head of the US Agency for International Development Andrew Natsios said recently that the UN fund should be used almost entirely for prevention rather than drugs.
He argued that infrastructure problems in Africa would reduce the efficacy of any drugs regime.
UNAids head Dr Peter Piot, however, has tried to cool the debate. He said the dichotomy between prevention and treatment is over.
Dr Piot is emphasising the fact that for the first time there will be a political declaration stating the importance of both prevention and treatment.
