The man who has been leading the World Health Organization's fight to stop bird flu from spreading has died after undergoing emergency surgery for a blood clot in his brain.

Dr. Lee Jong-wook, who was operated upon in Geneva Saturday, died Monday morning. The South Korean scientist was 61.

Lee Jong-wook was the first South Korean to head a UN body.
(Associated Press/Martial Trezzini)

"All of the staff of the World Health Organization extend their most sincere condolences to Dr. Lee's family," the United Nations agency said in a statement. "The sudden loss of our leader, colleague and friend is devastating."

Lee took over as director-general of the 2,400-employee WHO in 2003, when Severe Acute Respiratory Syndrome was the planet's major threat to public health.

The tuberculosis expert was the first person from South Korea to head a UN body. In 2004, Time magazine included him on its annual list of the world's most influential people.

In the past three years, Lee had been at the forefront of efforts to prevent an avian influenza pandemic from taking hold.

Under his leadership, WHO announced in late 2005 that it would stop hiring smokers as part of its campaign to eradicate the habit.

Anders Nordstrom of Sweden will replace Lee at the helm of the World Health Organization until a permanent successor can be named.