United Nations ? A top U.N. public health expert warned Thursday that a new influenza pandemic could come anytime and claim millions of lives unless officials take action now to control an epidemic in Asia.

Dr. David Nabarro, of the World Health Organization, called on governments to take immediate steps to address the threat at a news conference after his appointment as the new U.N. coordinator to lead a global drive to counter a human flu pandemic.

“We expect the next influenza pandemic to come at any time now, and it’s likely to be caused by a mutant of the virus that is currently causing bird flu in Asia,” he said.

The H5N1 strain of bird flu has swept through poultry populations in Asia since 2003, infecting humans and killing at least 65 people, mostly poultry workers, and resulting in the deaths of tens of millions of birds. The virus does not pass from person to person easily, but experts believe this could change if the virus mutates.

The 1918 influenza pandemic killed more than 40 million people, and there were subsequent pandemics in 1957 and 1968, which had lower death rates but caused great disruption, he said.

In a new pandemic, Nabarro said, “the range of deaths could be anything between 5 and 150 million.”