The WHO said the woman died on Monday after falling ill with a fever on Jan. 12. It said she worked in a shop selling dry goods and added it had no evidence of exposure to diseased birds, but was investigating.

Bird flu has killed at least 83 people since it reemerged in late 2003, according to WHO figures.

Experts believe the H5N1 virus is contracted through close contact with sick birds, but fear that as the virus spreads it will mutate to enable it to spread easily from human to human, sparking a pandemic that could claim many millions of lives.

The death is the second in the Sichuan province this month.

The victims lived in prefectures around 150 km (90 miles) apart. The WHO said it was concerned that no outbreaks of bird flu in poultry had been confirmed in areas where they lived.

"WHO recommends that, in China, testing for possible H5N1 infection should be undertaken in all cases of severe respiratory disease having no alternative diagnosis, even when no poultry outbreak has been reported in the patient's area of residence," it said.

Chinese officials have said the high number of small family farms, a lack of well trained officials and the world's biggest poultry population will make it hard to contain the disease.

MARKETS WARNING

Asia remains the epicentre of the fight against bird flu, although the virus has this month killed children in Turkey as it spreads westwards to the edges of Europe.

The WHO highlighted the threat posed by traditional markets in Indonesia, after local tests showed a chicken seller was infected with the H5N1 virus.

Hariadi Wibisono, director of control of animal-borne diseases at the Health Ministry, said the 22-year-old man was being treated in a Jakarta hospital for bird flu patients.

The WHO called for preventive measures included limiting contact between humans and poultry in markets, as well as better access to water and improved waste management.

"Massive interaction between humans and live poultry takes place every day in wet, traditional markets here and it might be a potential transmission of avian influenza," Alexander von Hildebrand, the WHO's Southeast Asia regional adviser for environmental health, said in a statement.

A Japanese group helping defectors from North Korea said a woman in Pyongyang was infected with bird flu last month after chickens carrying the disease were found in the capital.

Lee Young-wha, head of Rescue the North Korean People! Urgent Action Network, said the woman was reported to have been admitted to a Red Cross hospital in December.

North Korea's state media said in November it was stepping up its efforts to counter an outbreak of bird flu, but no cases of human infection had been reported.