Nearly 10 million more people infected with the AIDS virus now meet medical standards for receiving HIV drugs, according to revised UN guidelines released on Sunday, which experts say could avert 6.5 million deaths or new infections by 2025.

But achieving this goal will be a challenge, as it will add some $2 billion a year to the bill to fight the 32-year AIDS epidemic, they acknowledged.

"Treating people with HIV earlier ... can both keep them healthy and lowers the amount of virus in the blood, which reduces the risk of passing it to someone else," the World Health Organization (WHO) said in new recommendations for combatting the HIV/AIDS pandemic.

Around 34 million people worldwide were living with the human immunodeficiency virus (HIV) in 2011, nearly 70 percent of them in sub-Saharan Africa, according to WHO statistics.

The UN agency's previous treatment guidelines, set down in 2010, called for drug initiation when the tally of CD4 cells -- the key immune cells targeted by HIV -- reached 350 cells or less per microlitre of blood.

Under this benchmark, 16.7 million people in low and middle-income countries were medically eligible last year to receive the drug "cocktail", which rolls back infection although it does not cure it.

Despite years of fundraising and efforts to build medical infrastructure in poor countries, only 9.7 million of the 16.7 million currently get the treatment.

On Sunday, WHO said that after weighing evidence for drug efficacy, benefits for the immune system and potential side effects, it recommended raising the CD4 threshold to 500 cells per microlitre of blood.

That means treatment should start at a much earlier stage of infection.

This, along with the recommendation to treat all infected pregnant women and children under five - as well as other vulnerable groups, regardless of their cell-count - brings the number of patients who are advised to take these drugs to some 26 million, the WHO said.

"These guidelines represent another leap ahead in a trend of ever-higher goals and ever-greater achievements," WHO chief Margaret Chan said.

"With nearly 10 million people now on antiretroviral therapy, we see that such prospects - unthinkable just a few years ago - can now fuel the momentum needed to push the HIV epidemic into irreversible decline," she added.

Michel Sidibe, who heads the UN's AIDS prevention agency agreed, telling AFP the new guidelines were "bringing us closer to what I would call the end of the AIDS epidemic."

The aim is to get at least 15 million HIV patients onto antiretroviral therapy (ART) by 2015 and, by 2025, reach 80 percent coverage of those then in need.

But both goals will require a major rise in funding.

"It's not coming for free," acknowledged Gottfried Hirnschall, the head of WHO's HIV/AIDS department.

Gradually adhering to the new guidelines will add 10 percent to the currently estimated $22-24 billion needed each year to fully respond to the global HIV/AIDS epidemic. That figure includes not only treatment but also prevention and diagnostics, he said.

In 2011, the actual global spending stood close to $17 billion.

"But the impact will be substantial," he said, stressing that "we are expecting three million additional deaths avoided between now and 2025, and 3.5 million additional new infections averted."

-- Pay now, or pay forever --

Sidibe meanwhile said he believed that rather than growing, the costs of treating HIV patients would soon begin shrinking as drug and diagnostics prices continue their decline - and as countries find smarter ways of delivering the treatment.

Many countries "are really seeing the benefit of putting their people on treatment," he said.

"Fewer deaths, less sickness," took a burden off the healthcare system and meant HIV patients could remain in the workforce and contribute to the economy for longer, he pointed out.

This, in addition to the belief that more treatment will help avert infections, eventually leaving fewer people to treat, makes the investment a no-brainer, Sidibe said.

"If we do not pay now, we will pay later, we'll pay forever," he said.

The world has already scaled up treatment dramatically.

ART has reached 30 times more people last year than a decade earlier, when only 300,000 people in low and middle-income countries were receiving the then exceedingly expensive drugs, said Gundo Weiler of WHO's HIV/AIDS department.

"Over the last decade, the scale-up of antiretroviral treatment in low- and middle-income countries has averted 4.2 million deaths," he said.

Efforts to avoid mother-to-foetus transmission of the disease had also helped 800,000 children escape infection.

But Weiler and others warned Sunday that children infected with HIV were still one of the main groups left out with only one of three children needing antiretroviral treatment receiving it, according to 2011 statistics.

"It's not all rosy," Chewe Luo of the United Nations Children's Fund (UNICEF) said, calling for a "paradigm shift and some rethinking" of how to better treat children.