Japan is the latest Asian country to report an outbreak of bird flu

The WHO has been investigating the deaths of a number of people from a form of influenza in Hanoi.

"The current evidence does suggest a link between the chicken influenza and at least three of these cases," the WHO's Peter Horby said in Hanoi.

It comes as Japan has also confirmed a bird flu outbreak among its chickens.

It is the latest incident of the disease in Asia, which sparked panic when six people apparently died from the illness after contracting it from chickens in Hong Kong in 1997 and 1998.

Vietnam confirmed last week that it had an outbreak of the disease among chickens in the south of the country and has culled hundreds of thousands of birds to try and prevent the spread of the illness.

Close contact

The cull was being carried out with particular urgency because of the Lunar New Year, or Tet, holiday at the end of the month, when chicken is a popular dish.

But it now appears that the deaths in Hanoi could have been linked.

The only way to control the disease in chickens and humans...is to eradicate the infected flocks Peter Horby WHO

"At least three of the cases were due to... a particular strain of influenza called H5N1, which is the same type of influenza which has been reported as causing the deaths in chickens," Mr Horby told the BBC's East Asia Today programme.

H5N1 is the same strain that caused the deaths in Hong Kong five years ago.

Mr Horby said that any infected humans would have caught the illness from close physical contact with sick birds rather than eating them.

And he supported the Vietnamese authorities decision to carry out a cull.

"The only way to control the disease in chickens and humans... is to eradicate the infected flocks," Mr Horby said.

Trade

The Japanese authorities are now trying to establish the exact strain of the virus which has broken out in the Yamaguchi prefecture in the south of the country killing 6,000 birds.

Officials said that the virus found in the dead chickens was a strain of H5, but it is not yet known whether or not it is H5N1.

All the other chickens on the Yamaguchi farm will be destroyed and the trade in poultry and eggs from the area has been stopped.

The last recorded case of bird flu in Japan was in 1925.