Bird flu (search) can be expected to spread to other countries, but the biggest threat of it mutating into a human virus that could kill millions across the world remains in Asia, the World Health Organization (search) said Monday.

Tests on birds from Romania confirmed the arrival of bird flu in Europe on Saturday, two days after it was verified on Europe's doorstep in the Asian part of Turkey.

The U.N. health agency emphasized that while the arrival of the bird virus in Europe complicates efforts to stamp it out, the aggressive response by Turkey and Romania was reassuring.

The bulk of the problem is in Asia, where the virus has become endemic in some areas, creating multiple opportunities for a human pandemic strain to emerge, WHO said.

"There's no question that we will expect further outbreaks of avian disease in different countries," said Dr. Michael Ryan, director of the Department of Epidemic and Pandemic Alert and Response at the WHO. "Certainly North Africa and other countries in the African region are potentially in line for the introduction of the avian disease."

He added, "These introductions in Europe do represent a worrying development. We may see introductions into further countries over the coming weeks."

However, he said, "The problem is still very much focused in Asia."

In Hanoi, Vietnam, the United Nations' point man on bird flu told The Associated Press the world is not ready to cope with a potential pandemic that would skip across borders and oceans.

Dr. David Nabarro, the U.N. coordinator for bird and human influenza, said a pandemic could cause "billions, even trillions" of dollars in damage.

"I think that this is a very strong set of economic arguments that do mean that it is right for the world to invest quite generously in the actions required to both delay the pandemic and, then if it comes, to make sure we're ready for it," he said.

"I think that the world is now aware of the scale of the problem and is going to put in the resources."

As the H5N1 (search) virus is detected in poultry in new countries — the latest being Turkey and Romania — Nabarro said it was reasonable to believe that more poultry infections could occur along natural bird migratory routes in Europe, the Middle East and Africa.

Bird flu has killed more than 60 people in Southeast Asia since late 2003. Most cases have been traced to contact with birds, but experts fear a genetic mutation could spark a global pandemic.