Authorities in eastern India say bird flu is spreading through poultry flocks in the same area of West Bengal state where the virus was thought to have been brought under control a month ago.

Nearly four million chickens were slaughtered in last month's attempt to suppress avian influenza, and sales or transport of poultry were banned throughout West Bengal state. The area borders Bangladesh, which also has been battling the deadly poultry disease.

Sunday, government officials in West Bengal said laboratory tests have confirmed the infection is present in two villages about 300 kilometers from Calcutta, the state capital. The deadly H5N1 variety of bird flu has killed nearly 1,000 birds in the area in the past week.

No human cases of bird-flu infection have been reported in India.

However, West Bengal officials say they will continue testing blood from people with flu-like symptoms, to make sure the virus has not spread to people.

The World Health Organization says bird flu has killed 224 people around the world since 2003.

Some information for this report was provided by AFP and AP.