BARCELONA, Spain -- Doctors, medical researchers and grass-roots campaigners gathered here Sunday for a six-day assessment of the global AIDS pandemic, now spreading fast into Eastern Europe and Asia as it enters its third decade.

Around 15,000 people were to take part in the conference, the 14th in the series, including senior figures in the anti-AIDS campaign such as former U.S. President Bill Clinton and former South African leader Nelson Mandela. Opening ceremonies were scheduled to start at 1730 GMT with a performance by a local theatrical group and keynote speeches on the conference, whose theme is "knowledge and commitment for action."

The conference was previously staged annually but is now held every two years because progress has been so disappointingly slow.

It is an eagerly-awaited opportunity to swap the latest knowledge on the human immunodeficiency virus (HIV), which cripples the immune system and leaves the body exposed to opportunistic disease.

In the runup to the conference, campaigners were given a mixture of good and bad news about the battle.

A new report by the UN agency UNAIDS, which is a coorganizer of the Barcelona conference, said that 20 million people had already died since HIV was identified two decades ago, and another 68 million were at risk of heading for an early grave by 2020.

The virus has already steamrollered outhern Africa, and the report warned that it was making terrifying inroads into former communist Eastern Europe and Asia.

"The AIDS epidemic is still at an early stage. We knew it was the case for Asia and the former Soviet Union," Peter Piot, UNAIDS executive director, told AFP.

"But in addition it shows no sign of running out of steam in the worst-hit countries, in other words in Southern Africa," he said.

But campaigners also took heart in a decision by South Africa's constitutional court, which on Friday ordered the government to make anti-retroviral drugs available to pregnant women with the virus.

No vaccine or cure exists for AIDS, although anti-retrovirals can suppress HIV levels in the blood to indetectable levels and prevent a pregnant mother from infecting her foetus.

In previous years, the big row in the aids campaign has been the cost of these drugs, whose price had put them out of reach for sub-Saharan Africa, the worst-hit area.

Pressured by activists, Western pharmaceutical companies have slashed the prices of these treatments, and in some cases are offering to give them free to the poorest countries.

The chairman of the Barcelona conference, Jordi Casabona, indicated on Friday that further agreements on pricing for developing countries would be unveiled this week.

However, the situation is fast emerging of a two-tier price structure in which HIV patients in the Northern hemisphere are still paying high prices for the drugs.

A campaign group, AIDS Therapeutic Treatment Now (ATTN), was to stage a protest on sunday to demand lower prices in rich countries and unfettered access to copycat "generic" drugs in developing nations.

Sub-Saharan Africa accounts for some 70 percent of the 40 million people with HIV, but only 30,000 currently have access to anti-retrovirals, UNAIDS said.

"Despite the lowering of prices by nearly 90 percent of the anti-retrovirals, the vast majority of those in need have no access," Piot said.

He said 10 billion dollars was needed every year for about 10 years to seriously fight the scourge of HIV/AIDS in the most badly hit nations.