The increase in use reflects deep cuts in the price of branded medicines and widespread availability of cheap generics.

The total represents 31 percent of the 9.7 million people living with HIV in low- and middle-income countries who need the treatment, officials said. Most live in sub-Saharan Africa.

"The answer to the HIV epidemic is preventing new infections," said WHO HIV/AIDS Director Kevin De Cock. "An additional 1 million people came on to therapy but another 2.5 million became newly infected with HIV, so we have to do better with prevention."

The WHO report estimated that meeting universal prevention and treatment targets means funding would have to quadruple to $35 billion in 2010 and $41 billion in 2015.

The AIDS virus infects an estimated 33 million people globally, mostly in poor, sub-Saharan Africa, and has killed 25 million.

There is no cure or vaccine but antiretroviral therapy -- suppressing replication of HIV by interfering with its genetic workings -- can keep people healthy for years even if they never eradicate the virus. This means people must take them for life.

Leading manufacturers of AIDS drugs include GlaxoSmithKline, Gilead, Roche, Pfizer, Merck Inc, Bristol-Myers Squibb and Abbott Laboratories.

The WHO also reported progress in preventing HIV in children with nearly 500,000 women receiving AIDS drugs to prevent transmission to their unborn children.

This was up from 350,000 in 2006, although diagnosing HIV in infants remains a major hurdle, the WHO said. During the same time period, 200,00 children got antiretroviral drugs, up from 127,000 a year earlier.

"There is a long way to go but it is a substantial increase," De Cock said in a telephone interview.

While price cuts have helped make the life-saving drugs more widely available, crumbling health systems in poor countries pose a major challenge, De Cock added.

In particular, difficulties in training and retaining health care workers due to a "brain drain" of the most skilled personnel to richer countries will slow future delivery of drugs, the WHO said.

"Obstacles include weak health care systems, a critical shortage of human resources and a lack of sustainable, long-term funding," the WHO report said.