"We have seen evidence from nasal swabs taken from pigs in the Hanoi area that H5N1 is present," Anton Rychener, head of the UN agency in Vietnam told AFP. "We are now studying what the best course of action is."

The World Health Organization has warned that the H5N1 strain of bird flu 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.

Vietnam has around 25 million pigs but so far farmers in areas where poultry have fallen ill have not been instructed to slaughter them.

More than 14 million birds out of an estimated 250 million have died or been destroyed in an attempt to prevent further transmission of the disease, which has rapidly spread to 56 of the communist nation's 64 regions.

So far the WHO says it has no concrete evidence of human-to-human transmission. But it has warned it could not rule out the possibility that two Vietnamese sisters who died on January 23 could have been infected by their dead brother.

Of the 17 people confirmed to have been infected with H5N1 in Vietnam, two have made a complete recovery, but an eight-year-old girl and a 20-year-old woman remain hospitalised.

The FAO's Rychener said assurances given Thursday by Bui Quang Anh, director of the agriculture ministry's veterinarian department, that bird flu would be brought under control by the end of February were wildly optimistic.

"This is just not realistic. It is a political statement. I think bird flu will stay with Vietnam for good. It will be a permanent fixture and the only answer is to vaccinate all chickens," he said.

"I believe Vietnam's long term strategy must be to control the infection and then restock with vaccinated poultry."