Dr. Lee Jong-wook had been pushing for a coordinated global response to prepare for a mutation in the bird flu virus that could make the disease pass easily among humans and set off a potentially deadly pandemic.

The opening of the meeting was overshadowed by the news that Lee Jong-wook, the 61-year-old director-general of the World Health Organization, had died 2 1/2 hours earlier after undergoing emergency surgery for a blood clot in his brain.

Lee, a South Korean, "was an exceptional person and an exceptional director-general," said Elena Salgado, Spain's health minister and president of the assembly, in announcing the death.

UN Secretary-General Kofi Annan said Lee was "a great man" who "tackled the most difficult problems head on."

Preventing Bird Flu Pandemic

Lee had been pushing for a coordinated global response to prepare for a mutation in the bird flu virus that could make the disease pass easily among humans and set off a potentially deadly pandemic.

WHO members last year adopted a plan to implement by the summer of 2007 a fast-reporting system to guard against the start of a flu pandemic. The assembly is expected to take up on Tuesday a resolution under which nations can voluntarily implement the next reporting system immediately.

Lee, who took over WHO in 2003 as it wound up its battle containing SARS -- or severe acute respiratory syndrome -- quickly had to redirect the world's attention to bird flu.

The six-day meeting attended by more than 100 health ministers and other high officials rejected Taiwan's 10th bid for observer status, which the self-ruling island says would allow it to better join in efforts to contain disease outbreaks like bird flu.

China strongly opposed the proposal. The large majority of member countries accept Beijing's "one China" policy, which holds that Taiwan is a Chinese province and not a separate nation.

WHO officials note that Taiwan's government already can work with the agency in fighting disease under a 2005 agreement with China that confirms WHO's ability to send in experts to Taiwan in emergency situations.

Eradication of Polio

The meeting will discuss efforts to eradicate polio after the setbacks of last year when the disease re-emerged in a some countries. The assembly is expected to urge countries still afflicted with the disease to step up efforts to combat it and to encourage neighboring countries to respond promptly to any suspected cases.

The assembly also will study efforts to provide universal access to care for people infected with the AIDS virus.

Later in the week the assembly will take up a long-standing proposal to destroy the stocks of the smallpox virus still held by laboratories in the United States and Russia.

Mike Leavitt, US secretary of health and human services, said Washington continued to oppose the destruction of the virus.

"We believe that there is important scientific reason for that virus to continue to be studied and developed," Leavitt told reporters. "We are working at our Centers for Disease Control to develop improved ways in which we could respond to a reemergence of that virus and we continue to believe it has important scientific value."