A deadly strain of bird flu has been found in initial tests of several Vietnamese pigs, the Food and Agriculture Organisation says, but a Vietnamese government official says they are unaware of any such finding.
"The H5N1 virus was in the nasal cavities of the pigs," said Mr Anton Rychener, Vietnam representative of the UN agency. He added that blood tests on the pigs had been sent to Hong Kong and results were not yet returned. The pigs had not fallen ill with the virus that has killed at least 18 humans.
The finding is alarming because pigs can become a "mixing vessel" for the flu virus. The immune system of pigs is similar to that in humans and the animals suffer from a wide variety of diseases that also infect people.
Scientists say the bird flu pathogen could swap genes with a human influenza virus inside a pig.
The World Health Organization has said this could result in the emergence of a new subtype of virus for which humans would have no immunity.
Mr Rychener said three or four pigs were initially positive for the virus and that he did not recall how many swine in total had been tested.