The agriculture ministry in Japan has confirmed a third case of the bird flu virus at a farm in Kyoto.
FAO says without concerted effort, it will take several years to wipe out bird flu in Asia
Officials said more than 60,000 chickens have died at the farm in the past week.
The governor of Kyoto said despite the number of deaths, the farmer had not informed police and had gone on sending birds to a processing plant.
Ten Asian countries have so far been affected by bird flu, with at least 22 people killed in Vietnam and Thailand.
Japan had hoped to declare itself free of the virus, after gong almost a month without any new cases, since the first outbreak in mid-January.
But it has now suffered two more outbreaks, and there is a fourth suspected case under investigation in central Nagano province.
Animal experts meeting in Bangkok to discuss combating the disease said it would cost the minimum of $500m to stamp bird flu out in Asia and restock the region's poultry flock.
At the end of a three-day meeting, the head of the UN's Food and Agriculture Organisation(FAO) said most of that amount will have to be shouldered by the nations battling the disease.
"The largest amounts are obviously required at the country level where culling operations are going on and compensation has to be paid and restocking has to be made. That is where hundreds of millions of dollars will be required," said Samuel Jutzi, head of animal health at the FAO.
World animal health experts and officials from 23 Asia-Pacific countries, as well as international aid donors at the meeting agreed to increase efforts in fighting the disease and quicker steps in combating outbreaks.
Aid donors have pledged $10m to help among other things, improve surveillance networks and setting up a regional coordinating body in combating the disease.
Although previous bird flu outbreaks in Europe and the United States took six months to be wiped out, in Asia it is proving difficult despite massive culling.
Animal health officials expect it will take at least a year, or perhaps longer before Asia is free of the disease.
"If there is no change in the intensity of the campaign and there is no international mobilisation to help the countries, it will take several years," said the head of the FAO's Animal Health Service, Joseph Domenech.