After two days of emergency talks in Rome, the UN Food and Agriculture Organisation (FAO) urged governments to launch a vaccination campaign to contain the spread of avian influenza, which has struck 10 Asian countries.
"The epidemic has not been brought under control and we need an urgent response," said FAO Director Jacques Diouf, adding that the disease must be prevented from spreading geographically and to other animal species.
The warning came as traces of the highly pathogenic H5N1 strain of bird flu were discovered in pigs in the Vietnamese capital and its surroundings.
"We have seen evidence from nasal swabs taken from pigs in the Hanoi area that H5N1 is present," Anton Rychener, head of the FAO in Vietnam said. "We are now studying what the best course of action is."
The World Health Organisation (WHO) has warned that H5N1 could kill millions across the globe if it combined with a human influenza virus to create a new highly contagious strain transmissible among humans.
This situation could be exacerbated if pigs are found to carry H5N1 as they are an ideal "mixing vessel" for bird and human
viruses, experts say.
Rychener said bird flu had been detected in non-poultry animals in previous bird flu outbreaks around the world.
Peter Cordingley, spokesman for the WHO's Western Pacific Office in Manila, said the organisation was unable to provide any immediate comment on the potential impact on human health this new development could have.
"The epidemic has not been brought under control and we need an urgent response"
Taiwan, meanwhile, ordered a cull of 230,000 chickens on Friday after fresh outbreaks of the less virulent H5N2 flu strain were found at eight farms.
About 98,000 birds were slaughtered after earlier outbreaks, but so far the island remains free of the H5N1 virus, which doctors said on Friday had claimed another life in Vietnam.
New victim in Vietnam
The victim, a six-year-old girl from southern Dong Nai province, died on Tuesday at Ho Chi Minh City's Paediatric Hospital No1, becoming the communist nation's 13th victim from 17 confirmed infections. Thailand, where five people have died, is the only other country to have confirmed human infections.
So far the WHO says it has no concrete evidence of human-to-human transmission. It says contact with sick poultry is the main cause of infection.
An Australian microbiologist said on Friday although the chances of a new pandemic strain arising from a mix of human and bird flu viruses were "very small" they were greater than at any time since the last pandemic in 1968.
Experts say migratory birds may be
spreading bird flu virus across Asia
"Things are happening with the bird flu which are unprecedented and we have far more outbreaks and in more countries than is usual," Professor John MacKenzie from the University of Queensland said.
"I think this is the worst scenario possible and it does concern me enormously."
SARS a wake-up call
He described Severe Acute Respiratory Sydnrome (SARS), which killed nearly 800 people worldwide, as "a wake-up call" about what could happen with the flu.
Health experts meeting in Rome called on Thursday for a targeted vaccination campaign that would create a buffer zone around an affected region and the continued cull of birds in order to contain the disease.
But they also strongly criticised Asian governments for failing to report outbreaks quickly enough, and said greater transparency was essential.
"Things are happening with the bird flu which are unprecedented and we have far more outbreaks and in more countries than is usual"
Professor John MacKenzie,
University of Queensland
The FAO said an emergency regional meeting would take place at the end of the month in Thailand to coordinate implementation of the Rome recommendations.
China is one of the countries facing charges of covering up bird flu outbreaks. Thirteen of the country 31 regions were host to either suspected or confirmed cases, but the goverment has insisted there are no human infections.
South Korea, meanwhile, began culling 30,000 chickens and ducks after a new bird flu outbreak was discovered at two farms south of Seoul.
Singapore has so far maintained that it is free from the disease, but local media reported on Friday that 30 birds had mysteriously died.
Although global health authorities are unsure about the origin of the virus, they have said migratory birds may be spreading it across Asia.