GENEVA (Reuters) -- Surveillance for the HIV virus is weak in most of the world and prevention and treatment programs often fail to reach high-risk groups the World Health Organization said on Friday.

In a message marking World AIDS Day, being celebrated under the theme of Accountability, the WHO's acting director-general Anders Nordstrom said that tackling the AIDS epidemic remained one of the world's most pressing public health challenges.

Only 1.6 million people or 24 percent of the 6.8 million people worldwide who need the life-extending therapy receive it, according to the latest joint report of UNAIDS and the WHO. Nearly 40 million adults and children are infected worldwide and HIV infection is rising in every region of the world, especially in east Asia and in eastern Europe/central Asia, according to the latest UNAIDS/WHO report.

Louise Arbour, UN High Commissioner for Human Rights, reminded governments of their duty to increase access to anti-retroviral drugs for all AIDS sufferers, without discrimination.

UN Secretary-General Kofi Annan said AIDS has become the greatest challenge of the generation, but for far too long the world had been in denial about the epidemic which emerged 25 years ago. "Accountability -- the theme of this World AIDS Day -- requires every President and Prime Minister, every parliamentarian and politician, to decide and declare that 'AIDS stops with me'," Annan said.