Health experts on Thursday called for trials of an HIV vaccine under development in Thailand to be speeded up following recent setbacks in other efforts to end the AIDS epidemic.

Initial test results of the RV144 vaccine -- jointly developed by US military researchers and the Thai health ministry -- in 2009 found a 31 percent protection rate among 16,000 Thai volunteers.

Phase IIb trials could start next year in the kingdom, a major forum in Bangkok heard.

Experts are optimistic a modified version of the vaccine will raise the protection rate to around 50 percent -- the figure needed to obtain regulatory approval for public release.

"After 30 years of this epidemic we're closer to a vaccine than we ever have been," Mitchell Warren, of US-based AVAC Global Advocacy for HIV Prevention, told AFP at a forum in Bangkok.

"But it's important we don't let our efforts slip. The challenge now is to make sure we take the next steps quickly," he said.

He said the next tests would take one or two years. After that comes Phase III, the widest and most exhaustive trial stage.

Experts at the Aids Vaccine Efficacy Consortium in the Thai capital said the vaccine could be available by 2020 if tests are speeded up in Thailand, as well as in South Africa where parallel research is planned.

Thailand has pledged to establish a public-private company to manufacture the vaccine if trials are successful.

The kingdom became a research hub for the illness after high rates of HIV were detected among army recruits in the 1990s, and has been praised for its proactive approach to prevention, awareness-raising and treatment of the illness.

However the World Health Organisation says Thailand still has more than 520,000 people living with HIV and AIDS -- the highest number in Southeast Asia.

HIV rates are rising among high-risk groups such as gay men, who saw an increase from 24.5 percent in 2005 to 29.4 percent in 2011, according to US and Thai health authorities.

There is currently no vaccine against HIV on the market, and no cure for AIDS, which has killed some 35 million people around the globe.

US authorities announced in April they had halted clinical trials of an experimental vaccine called HVTN 505, which was the latest in a series of unsuccessful studies.

Any successful vaccine must be speedily targeted at high-risk communities particularly in the Asia-Pacific region where rates are bucking a global downward trend, according to Luiz Loures of UNAIDS.

"But we can end AIDS," he added. "For the first time we've started to see that the end of AIDS is a real possibility."