HANOI - A 15-month-old girl and a man are the latest suspected cases of bird flu infection in Viet Nam, a senior health official said on Wednesday as attention turned to pigs as possible carriers for the illness.

Both patients are suspected of contracting avian influenza strain A, also known as H5N1, Dau Ngoc Hao, deputy director of the Agriculture Ministry's Veterinary Department in Hanoi, said.

They were among 15 people who fell ill with influenza in Hanoi and surrounding provinces. Twelve, most of them children, have died.

The World Health Organization said on Tuesday tests conducted by a Hong Kong laboratory had confirmed that bird flu killed three of the 15.

Hao suspected pigs were playing a role in the transmission of bird flu to humans.

"It is possible that the bird flu virus spreads from chickens to pigs before jumping to humans," he said, but did not elaborate.

Local officials said ducks and pigs were also dying in southern provinces.

By Wednesday, the virus has killed nearly 1.4 million chickens in the southern provinces of Long An and Tien Giang.

"The situation in southern Viet Nam is still very complicated," Hao said.

Peter Cordingley, a spokesman for the WHO's Western Pacific headquarters in Manila, said: "We're worried that the virus will latch on to a normal human influenza virus, which is extremely contagious, and then we'll have a big problem."

Cordingley stressed there was "no evidence of human-to-human transmission" among the Viet Nam flu victims.

"While there are people falling sick inside families, it's more likely that the transmission - if it comes from anywhere - comes from the chickens," he said.

Hanoi declared last week that it had been struck by a fast-spreading bird flu that has hit other countries in Asia, which has a vast poultry industry.

South Korea, which has already culled nearly 2 million chickens and ducks, reported last Tuesday the first new case of avian flu in more than a week, dashing hopes that the outbreak was subsiding.

Virulent strain

Hundreds of people living in affected areas have been given blood tests, although a health official said no one had shown symptoms of the disease.

Japan reported its first bird flu outbreak in years on Monday.

Thailand, which produces about 1 billion chickens a year and exports mainly to Japan and Europe, said it was free of bird flu but was battling an outbreak of poultry cholera.

"I would like to insist that Thailand is free of bird flu," said Nirundorn Aungtragoolsuk, director of the Agriculture Ministry's Livestock Disease Control Division.

The government has destroyed hundreds of thousands of chickens since November to stop the spread of a virulent strain of poultry cholera, known as Pasteurella Multocida Type A, which cannot spread to humans, Nirundorn said.

The bird flu scare had no impact on shares in Thailand's major chicken exporters, but some neighbouring countries are taking no chances.

Deeply impoverished Cambodia, sandwiched between Viet Nam and Thailand, said it had banned poultry imports from neighbouring countries last week and sent experts to its chicken farms.

(Agencies via Xinhua)