'We have killed all the chickens in suspected areas after lab tests confirmed that a small flock of native chickens raised by a farming family died of H5N1,' an official at the Agriculture Ministry's department of livestock told Reuters.

It was the fourth case of the deadly virus found in Thailand in 10 months.

On Tuesday Agriculture Minister Somsak Prisnanantakul confirmed the virus had been found in Sukhothai, 400 km (250 miles) north of Bangkok, and more than 200 chickens were culled.

There were four outbreaks in Thailand last year but there have been no reports of human infection in the country since September 2006.

The H5N1 virus has killed 17 people in Thailand since 2003 and 245 people in total out of 387 confirmed infected around the world, according to the World Health Organisation.

It is endemic in poultry in parts of Asia.

Scientists fear the H5N1 virus could mutate into a form that could spread easily among humans and kill millions of people. -- REUTERS