A total 236,000 poultry within a 500-meter (1,650-foot) radius of the outbreak site in Iksan, about 250 kilometers (155 miles) south of Seoul, will be slaughtered to keep the virus from spreading, ministry official Kim Chang-sup said.

The outbreak occurred last week, resulting in the deaths of 6,700 infected chickens. Another 6,300 were culled.

South Korea killed 5.3 million birds during the last known outbreak of bird flu in 2003.

The H5N1 virus began ravaging Asian poultry stocks in late 2003 and has killed at least 153 people worldwide.

So far, the disease remains hard for people to catch, and most human cases have been traced to contact with infected birds. But experts fear it will mutate into a form that is easily spread among people, possibly creating a pandemic that could kill millions.

Also last week, a low-grade strain of bird flu killed 200 chickens in a separate outbreak south of Seoul. The Agriculture Ministry said it was not the H5N1 strain, which unlike most bird flu viruses is harmful to humans.