High rates of HIV infection combined with rapid population growth mean the next half-decade will be critical for rolling back AIDS, specialists warned on Thursday.

"The next five years provide a fragile window of opportunity to fast-track the response and end the AIDS epidemic by 2030," said Michel Sidibe, head of the UN agency UNAIDS.

"If we don't, the human and financial consequences will be catastrophic."

A report compiled by UNAIDS and The Lancet medical journal, with the support of leading figures in the 34-year war on AIDS, called for the disease to be given high priority in the UN's post-2015 development goals.

It pointed to good news, beginning with the advent in 1996 of antiretroviral drugs, which suppress the human immunodeficiency virus (HIV).

Though not a cure, the therapy creates a virtuous circle, scientists have found. The less virus in circulation, the less likely it is that people become infected.

"From 2001 to 2013, annual incidence of HIV infections decreased by 38 percent, from 3.4 million in 2001 to 2.1 million in 2013," said the report.

"From 2002 to 2013, the annual incidence of HIV infections in children decreased by 58 percent, with 240,000 new infections in 2013 compared with 580,000 in 2002. In some parts of the world, mother-to-child transmission of HIV has been virtually eliminated."

In South Africa, one of worst-hit countries, mean life expectancy rose in 2005 for the first time since 1997.

But there remain many concerns, said the report, carried in The Lancet.

In 2013, 1.5 million people died of AIDS-related causes, more than 10 million infected people had yet to start HIV therapy -- and out of 35 million people estimated to be living with the AIDS virus, a massive 19 million did not know they were infected.

This means that, despite the gains, the rate of HIV infections is still not falling fast enough.

- 'Stark truths' -

Coupled with growth in the world's population, as more people enter adolescence and become sexually active, this imperils the objective of eliminating AIDS as a public health threat by 2030.

"We must face stark truths," said Peter Piot, director of the London School of Hygiene and Tropical Medicine and Sidibe's predecessor at the helm of UNAIDS.

"Expanding sustainable access to treatment is essential, but we will not treat ourselves out of the AIDS epidemic.

"We must also reinvigorate HIV prevention efforts, particularly among populations at highest risk, while removing legal and societal discrimination."

The report also highlighted the need to ramp up funding.

Current efforts cost in the order of $19 billion (17 billion euros) per year, "whereas it will take $36 billion annually to achieve the UN goal" for 2030, it said.

In poor, badly-hit African countries, the campaign will require as much as 2.1 percent of gross domestic product (GDP) annually and at least a third of government health expenditure.

"This clearly demonstrates that international support to the AIDS efforts in these countries will be needed for many years to come," the authors warned.