The world is losing the battle against HIV/Aids, US President George W Bush's top adviser on the virus has said.
Dr Anthony Fauci told a conference in Sydney that progress had been made but more people were being infected with HIV than were being treated.
"For every one person that you put in therapy, six new people get infected. So we're losing that game, the numbers game," he said.
Dr Fauci was speaking at a gathering of the world's leading HIV/Aids experts.
Last year, 2.2 million people in the developing world had access to the anti-retroviral drugs that help treat the virus, compared with less than 300,000 people three years ago.
"The HIV epidemic is essentially uncontrolled, uncontrolled in Africa, uncontrolled completely in Asia right now"
Dr Brian Gazzard
British HIV Association
But new infections were continuing to outpace the global effort to treat and educate patients, the conference heard.
Delegates were encouraged by findings that male circumcision can reduce the risk of HIV infection in young men by 60%.
The study, based on trials in Kenya, Uganda and South Africa, forecast that male circumcision would prevent 5.7 million new cases of HIV infection over 20 years in sub-Saharan Africa.
The number of people with HIV is expected to rise from around 40 million today to 60 million by 2015
Aids has already killed 25 million people
Only 28% of the world's HIV/Aids patients are on anti-retroviral drugs
Just one in 10 pregnant women with Aids get treatment to stop them transmitting the disease to their unborn children
"We've had one important breakthrough this year, with understanding the role of circumcision in prevention," said Dr Fauci, the director of the US National Institute of Allergy and Infectious Diseases.
"We need to do more of that and importantly, we need to make available to the people throughout the world the prevention methods that are proven technologies."
But in many parts of the developing world, effective prevention strategies like condoms and sterile syringes are available to less than 15% of the population.
Dr Fauci's warning at the Fourth International Aids Society Conference on HIV Pathogenesis and Treatment was echoed by other experts.
Dr Brian Gazzard, of the British HIV Association, said that despite greater access to anti-retroviral drugs, the disease was running out of control in parts of Asia and Africa.
"The HIV epidemic is essentially uncontrolled, uncontrolled in Africa, uncontrolled completely in Asia right now," he said.
The Australian conference's 5,000 delegates are drawn from more than 130 countries.
The red Aids ribbon, introduced in 1991, is now universally recognised
Here are some of the key dates in the history of the illness since then.
1982 - Aids, Acquired Immune Deficiency Syndrome, is first used as a term.
The condition had earlier been known as Grid - Gay Related Immune Deficiency.
The first case of Aids is reported in Africa.
1983 - The US Centers for Disease Control adds female partners to the list of groups at risk.
1984 - HIV (human immunodeficiency virus) is isolated by Luc Montagnier of the Pasteur Institute in Paris and Robert Gallo of the US National Cancer Institute.
1985 - Hollywood star Rock Hudson is revealed to have Aids.
1987 - The UK government's "Don't Die of Ignorance" campaign is launched.
Needle exchanges are first piloted in the UK.
The first antiretroviral drug, AZT, is approved in the US.
Pictures of Princess Diana holding the hand of a patient in an Aids ward are broadcast around the world.
HIV testing is introduced across the UK.
1988 - First World Aids Day.
1989 - The first HIV awareness materials targeted at gay men are produced by the Health Education Authority.
1990 - The BBC soap opera Eastenders runs a storyline in which Mark Fowler, a major character, is found to be HIV positive, raising awareness of the condition.
1991 - Freddie Mercury, lead singer of Queen, dies of an Aids-related illness.
The Red Ribbon becomes the international symbol of HIV.
The US Food and Drug Administration licences the first rapid HIV test.
Ten million people around the world are HIV positive. Aids kills more men aged 25 to 44 than any other condition.
1995 - There is an outbreak of HIV among injecting drug users in Eastern Europe.
The first combination therapy - HAART, (highly active antiretroviral therapy) is approved for use in the US.
1996 - UNAIDS is established.
1998 - Trials of a vaccine against HIV begin.
2001 - Drug companies abandon their opposition to the generic production of antiretrovirals.
2002 - The Global Fund for the fight against HIV/Aids, malaria and TB is set up.
2003 - Results of the first major HIV vaccine trial - Aids VAX - show promise.
2005 - International leaders commit to universal access to treatment at the G8 Summit in Gleneagles.
About 1.3 million people in developing countries have access to treatment.
2006 - About 38.6m people are estimated to be living with Aids worldwide.