China told the Uunited Nation's Food and Agriculture Organisation (FAO) it had confirmed a new outbreak of the deadly H5N1 strain of the disease in the city of Changji in the far western region of Xinjiang.
Scientists fear that bird flu, which is infectious in birds but does not spread easily among humans, could mutate and generate a pandemic, likely to start in Asia, that could kill millions of people.
The Washington Post reported on Saturday that Chinese farmers, acting with government approval and encouragement, had tried to suppress major bird flu outbreaks among chickens with the drug amantadine, possibly making it useless in fighting human influenza.
China's Foreign Ministry said on Tuesday the government had never given its approval for such treatment and vowed to investigate.
"We are not completely sure about how widespread (amantadine use in China) is, but it has not been a complete surprise to us that it has been used," WHO representative Henk Bekedam said.
Misuse of anti-virals
Misuse of anti-virals could make bird flu viruses, including the H5N1 strain, resistant to the drugs and give doctors fewer weapons to handle outbreaks among people.
"We know in general these resistances are gradually building up," Bekedam said.
"The part that concerns us is these things should not be unnecessarily speeded up. The use of anti-virals in agriculture needs to be very closely monitored. And the same thing for the use of anti-virals in humans."
"The part that concerns us ... is these things should not be unnecessarily speeded up. And therefore the use of anti-virals in agriculture needs to be very closely monitored. And the same thing for the use of anti-virals in humans"
H5N1 first surfaced in poultry in Hong Kong and China eight years ago and has killed at least 37 people in Vietnam, 12 in Thailand and four in Cambodia.
Vietnam reported on Monday that two more people had contracted bird flu in the country's north.
The FAO sought an official response on the amantadine issue on Tuesday and was told by China's Agriculture Ministry that a third outbreak was found in China that had infected 128 domestic birds, including 63 that died.
Call for concern
"The national reference lab diagnosed H5N1 again," FAO's representative in China, Noureddin Mona, said. He said FAO was told the outbreak was under control.
"It makes us very concerned," he said.
No human cases of bird flu have
been reported in mainland China
There have been no human incidents reported in China.
"But we have really to be prepared for something which we don't like," Mona said, adding that 1490 birds had been culled.
Representatives of the WHO and FAO and counterparts from China's health, agriculture and state forestry ministries on Sunday flew to China's western Qinghai province to inspect avian flu prevention efforts after wild birds killed by H5N1 were found in the region in May.
China successfully curbed an avian flu outbreak in Qinghai last year, culling thousands of birds.
No infections of domesticated birds or humans have been reported in the recent outbreak.