Cutting down on Aids funding would prove to be fatal for millions of patients who would have no acess to anti-retroviral (ARV) drugs, warned Medecins Sans Frontieres.
"Donors have started to shift their support away from HIV/AIDS, and funding is not keeping up with the need," the medical charity warned in a report ahead of a major AIDS conference in Vienna next week.
"If nothing is done, most of (those infected with HIV) will die within the next few years," it said, in a study based on fieldwork in eight African countries.
The Global Fund to Fight AIDS, TB and Malaria is trying to raise 20 billion dollars (15.5 billion euros) for the next three years.
So far it has received just a few hundred million dollars, the author of the report, Mit Philips, told journalists.
"It is a very frustrating feeling to see that in spite of the achievements that have been made... the international donors, for the moment, show less interest and less resolve to continue to support the fight against HIV/AIDS," she said.
"It's as if they want to give up the fight halfway through. We want to tell them: 'you cannot turn back now on AIDS treatment, it's too important'."
While some three million HIV patients now have access to anti-retroviral drugs in Africa, the continent worst affected by the virus, another six million were still without treatment, MSF warned.
By reducing funding, donor countries would ensure that even fewer patients received care, or received it too late, it added in its report.
Turning people away from clinics, for lack of staff or resources, would also destroy the sense of trust that took years to build with local communities and make people less willing to come forward and get tested in a region where HIV still carries a strong stigma.
MSF's study showed that early and sustained treatment of HIV patients had born fruit in several regions, including Malawi's Thyolo district where the overall death rate dropped by a stunning 37 percent between 2000 and 2007, thanks to universal access to ARVs.
Where patients get treatment, "there is an overall reduction of mortality in the community, there is also less tuberculosis and we start to see, where there is a high coverage of ARV, also a reduction in the number of new cases (of HIV/AIDS)," said Philips.