SEJONG (Yonhap) -- A bird flu case has been confirmed at a chicken farm in Gyeonggi Province the government said Thursday, a disturbing sign that all-out quarantine efforts are having limited impact.

The agriculture ministry said that tests showed a chicken breeding farm in Hwaseong came up positive for the H5 strain of avian influenza (AI) that is sweeping parts of the country. Past cases have been restricted to the Jeolla and Chuncheong region in the country's southwestern region.

"At present we are trying to determine if the latest case is a virulent AI strain," a ministry source said. He said that all poultry within a three-kilometer radius of the affected farm have been culled as a preventative measure.

This is the first time that a bird flu case has been detected so far north.

The Gyeonggi region that surrounds the capital city of Seoul is home to the largest number of chicken farms in the country.

The ministry said the farm affected by the outbreak is located some 15 kilometers southwest of Sihwa lake, a key stopping area for migratory birds.

The government suspects migratory birds have spread the latest outbreak. The virulent H5N8 strain of AI was identified in a group of wild ducks found dead Jan. 17 at a reservoir near a duck farm that first reported the disease.

Besides the latest outbreak, authorities confirmed separate H5 bird flu cases earlier in the day after farmers reported sick and dying birds on Tuesday. One case at a small-scale chicken farm in Miyang, South Gyeongsang also drew attention because it is a first for the region. Birds there have been confirmed to have contracted the virulent H5N8 strain of AI.