Agriculture officials in South Korea have confirmed that avian influenza was responsible for the deaths of thousands of chickens earlier this month.

The country began an investigation after 20,000 chickens died at a farm in Umsung, around 40 miles southeast of Seoul. A further 5,000 chickens at the farm were slaughtered in a move to try to stop the spread of the highly contagious bird flu. All poultry within a six-mile radius were also quarantined as a preventative measure.

Tests showed that this outbreak had been caused by the H5N1 virus, but as yet the authorities are not clear whether it is the H5N1-97 strain which crossed from chickens to humans in Hong Kong in 1997 leading to the deaths of six people, reported The Associated Press.