The top United Nations official handling avian flu says Asia has shown significant progress in preparing to fight the spread of the virus. But the official warns that more help is needed to support Indonesia, where a majority of the country's provinces have reported the presence of the disease.

United Nations officials say Asia needs to increasingly focus on medium- to longer-term efforts to control the spread of avian flu virus.

David Nabarro, the senior U.N. coordinator for avian and human influenza, says, overall, Asia has registered significant progress in the past year in preparing to stem the spread of avian flu.

Nabarro, and other U.N. officials, say Indonesia remains the key country of concern, and is in need of greater international assistance.

"Indonesia … there's a lot more to do," he said. "The challenge of improving animal health services, and also scaling up human health capacity, continues to be substantial in that country."

Indonesian chicken market workers walk past a stack of chicken cages at a market Tuesday Oct. 17, 2006 in Jakarta, Indonesia

Indonesia has recorded the highest number of human fatalities from bird flu - at least 55 deaths. Worldwide, the H5N1 strain of the virus has killed more than 150 people in nine countries since 2003.

Hiroyuki Konuma, deputy regional director for the U.N. Food and Agriculture Organization (FAO), says the disease is firmly established in Indonesia.

"The virus is widely spreading at the moment, and, according to the source of information from the FAO, out of 33 provinces, the majority of provinces have avian influenza problems," said Konuma.

Indonesia has been criticized for resisting mass culling of infected poultry. On Friday, officials there announced plans to ban city residents from keeping free-roaming backyard poultry, in a bid to prevent the virus spreading to people. But they did not say when the measure would come into effect.

Indonesia also says it has been improving bird flu education and awareness programs.

The U.N.'s Nabarro warned Friday that a bird flu epidemic among humans could begin anywhere, not just in countries like Indonesia that showed higher concentrations of the virus.

Nabarro is on his fourth visit to the region to review bird flu preparedness. He praised Vietnam and Cambodia for their avian flu preparations, and singled out Burma, also known as Myanmar, for its open and cooperative approach on avian flu issues.

"There has been total openness in communicating with the officials of the U.N. system on issues to do with avian influenza, and we are very satisfied with the way in which the Myanmar authorities responded," he said.

A key concern now for countries in the region is the approaching winter. The number of flu cases typically increases during the cold season, from November to February.

So far, most bird flu cases in people have been caused through contact with infected poultry, but scientists are concerned the virus could mutate into a form more easily spread among humans, possibly causing a pandemic.