UN Secretary General Ban Ki-moon said most countries have failed to live up to a commitment they made two years ago to fight AIDS and probably won't meet the UN AIDS Millennium Development Goal to reverse the spread of the disease by 2015.

In 2006, the United Nations General Assembly aimed to provide universal access to HIV prevention, treatment, care and support by 2010, he reminded the International AIDS Conference in Mexico City.

"Most countries still have a long way to go" to meet that goal, which will make it difficult to meet the 2015 target, he said in a text prepared for delivery to the meeting on Sunday. About 22,000 delegates are attending the week-long summit. The previous one was held in Toronto in 2006.

"We are still facing a huge shortfall in resources," and richer countries will have to help the poorest countries, which are worst-hit, Ban said.

But he singled out the United States for praise. "I warmly congratulate the United States government on the new legislation that will allow for $48 billion to be spent on the fight against AIDS, TB and malaria over the next five years."

Failing to make gains against AIDS will hurt other goals, such as reducing poverty, curbing the spread of malaria and strengthening health systems, Ban said.

Dr. Julio Montaner, a University of British Columbia expert who is to be the next president of the International AIDS Society, told CBC News that combination therapy, which includes prevention and treatment of existing cases, is a key topic at the meeting.

"We know how to do it. We should do it now," he said from Mexico City. There is not likely to be a vaccine or cure found in the near future, he added.

Demonstrators at the conference demanded "medication for every nation" and better access to drugs that slow the spread of HIV.

They said anti-retroviral drugs are too expensive, pushing them out of reach for too many.

About 33 million people are infected with AIDS, two-thirds of them in sub-Saharan Africa.