Seoul  - South Korean authorities said Friday they were employing all means possible to prevent the spread of avian influenza after reports of a new case of the dangerous animal disease.

Almost 300,000 birds at the affected chicken farm in the town Gimje south of the capital Seoul were being culled as a precautionary measure, a spokesman for the country's Agriculture Ministry said.

The highly contagious H5N1 virus strain was detected in dead animals at the chicken-breeding farm on Thursday, the first time the strain was detected in farm animals in South Korea in more than one year.

A quarantine zone was set up in a 10-kilometre radius around the farm in question and restrictions regarding poultry transport introduced in an even larger area, the ministry said.

It remained unclear how the animals contracted the disease. From November 2006 to March 2007, six bird-flu outbreaks were reported in South Korea, and 2.8 million birds were culled as a result.

In June, South Korea declared itself free of the H5N1 virus. (dpa)