World Aids Day on December 1 each year brings together organizations that have been fighting the disease that has killed more than 25 million people since the 1980s. The millions of people infected and living with the Aids virus bear the stigma of the disease, Ban said.

"Overcoming stigma remains one of our biggest challenges," Ban said in a prepared address to be delivered late Friday. "It is the single barrier to public action on Aids. It is one of the reasons why the epidemic continues to wreak its devastation around the world."

He said HIV/Aids is "unlike any other" disease because it is also a social and human rights issue, and an economic issue, targeting young adults at a time they can contribute to economic development, intellectual growth and childrearing.

The United Nations has called for halting the spread of the disease by 2015, but some countries have succeeded more than others in implementing national programmes in fighting Aids.

"We have made tangible and remarkable progress on all these fronts," he said. "But we must do more."

"On World Aids Day, let us show the leadership it takes to live up to our responsibility," Ban urged UN members.

The UN-Aids programme and World Health Organisation said in Geneva in November that more than 33 million people are currently living with HIV, the virus that causes Aids, down 16 per cent from last year's 39.5 million, after the two organisations revised the numbers.

Around 2.5 million new people will have been infected and 2.1 million will have died of Aids in 2007.

UN-Aids said the decline in Aids cases, which has been seen in the last two years, was in part due to the life prolonging effects of antiretroviral drugs therapy and to the success of HIV programmes.

UN-Aids Executive Director Dr Peter Piot said in Geneva, "These improved data present us with a clearer picture of the Aids epidemic, one that reveals both challenges and opportunities."

"Unquestionably, we are beginning to see a return on investment, new HIV infections and mortality are declining and the prevalence of HIV levelling," Piot said. "But with more than 6,800 new infections and over 5,700 deaths each day due to Aids we must expand our efforts in order to significantly reduce the impact of Aids worldwide."