China announced a sixth death from a new strain of bird flu Friday.
Authorities slaughtered more than 20,000 poultry at a Shanghai market where the virus was detected in pigeons being sold for meat.
The mass bird killing is the first so far as the Chinese government responds to the H7N9 strain of bird flu.
The virus has made 14 people ill, many of them critically, along the Eastern Seaboard. These are the first infections of people.
Gregory Härtl, spokesman for the World Health Organization, said there were no apparent links between the 14 reported cases of the bird flu strain, and there is also no evidence of sustained human-to-human transmission.
Härtl said Chinese authorities were monitoring 400 people who had been in contact with the patients.
He explained the virus could be spread from animals or from environmental factors.
"An environmental source can be animals but it also can be areas surrounding animals such as in the case of H5N1, where you have poultry markets. The virus often can attach itself to dust particles, so dust particles can be a transmitter of the virus, so to speak. This is why all avenues have to be followed up, and this is being done very actively," said Härtl.