China is dismissing international media reports that it encouraged its farmers to misuse a drug meant for humans by giving it to chickens as a guard against bird flu. But officials say they will investigate whether it is being used.

Reports, starting with one by the U.S. newspaper, the Washington Post, quoted researchers as saying the Chinese government has for years encouraged farmers to feed to chickens the anti-viral drug amantadine, which is meant only for humans. Experts say the action - which would violate international guidelines - may have rendered the drug useless against influenza.

In remarks carried by a state-run newspaper, China's agriculture ministry called the Post report "groundless." At a regular briefing, a foreign ministry spokesman, Liu Jianchao, denied that the government played a part, but said the general situation would be investigated.

"China's government never allowed any human anti-viral drugs to be used on poultry to prevent bird flu or other animal diseases," said Mr. Liu. "We have a responsibility to mankind and will seriously investigate this matter."

Amantadine is one of the few drugs available for treating influenza in humans. Researchers quoted by the Washington Post said the misuse of the drug had caused the appearance in Thailand and Vietnam of a form of the bird flu virus, known as H5N1, that is resistant to amantadine.

Other reports quoted a World Health Organization official as confirming that a resistant form of the virus has been observed.

Bird flu has killed at least 54 people who contracted it from infected birds in Cambodia, Thailand, and Vietnam during the past two years. Health officials are concerned that it could mutate to a form that would make it easier to transmit from human to human.

International health agencies have expressed concern over the report that the anti-viral drug was allegedly misused in China and say they are awaiting more information from Chinese officials. An official with the World Health Organization in Beijing said the agency had no comment on the Chinese government's denial of wrongdoing.