Launching his agency's 2008 report on the global AIDS epidemic, Peter Piot, UNAIDS executive director, urged more action to prevent the spread of the disease among gay men who have unsafe sex and stressed the importance of working with affected communities.
"All over Asia there are now epidemics of HIV in men who have sex with men of the same magnitude that we saw in this country 25 years ago," Piot said.
"That is something that has been detected fairly recently. There is not enough action yet but we are now starting programs," he added.
Paul De Lay, director of Evidence, Monitoring and Policy at UNAIDS, said the HIV epidemic among gay communities in Asia was not new, but that it had recently reached the levels seen in cities such as San Francisco at the end of the 1980s when HIV infections reached their peak.
He said it could be due to a number of factors, including less funding for programs that target men who have sex with men and the fact that there were new groups who were less aware of the risks of unprotected sex.
"Asia has recognized populations of men who have sex with men for quite some time," he told AFP. "The epidemic in these populations started in the mid-1990s. What we see now is a resurgence."
"There are countries where the percentage of people infected are similar to what we were seeing in San Francisco or in Berlin or in London where up to 15 to 20 percent of men who have sex with men are HIV positive," he added.
The report meanwhile noted that unprotected sex between men was a "potentially significant but under-researched aspect of the HIV epidemics in Asia," citing countries such as Thailand and Vietnam.
"Recent study data from several major cities in the region, from Bangkok to Ho Chi Minh City, show increasing HIV prevalence among men who have sex with men," the report said.
In China, unsafe sex between men could account for up to seven per cent of HIV infections, it noted.
De Lay said there were also high infection rates among gay populations in cities such as Chennai and Mumbai in India and in Indonesia's capital Jakarta.
He added that these communities often faced homophobia from the wider population, as well as discrimination from health care providers, which discouraged them from seeking information and getting tested.
"Even without blatant national laws that criminalize homosexual behavior, you can still have a gradation of policies and practices that can be almost as bad," he said.
De Lay pointed to a similar resurgence of HIV infections among gay populations in the US and western Europe, which he said showed the need for constant vigilance.
The report said higher risk unprotected sex among gay men in several countries in western Europe, such as Germany, appeared to be linked to the increasing numbers of new HIV diagnoses among that group.
"It's disturbing because it's this sense that we can never let our guard down as far as prevention, that the epidemic will come creeping back if there isn't this constant attention being paid to it," De Lay said.