One of five wild ducks found dead in South Korea this week was on Saturday confirmed to have been infected with a lethal strain of the bird flu virus as the country battles its first outbreak in over two years.
Tests showed the five dead birds found in Sacheon City on December 26 had been stricken with the H5N1 virus, the agriculture ministry said in a statement.
The same strain - which poses a risk to humans - has also been detected in wild birds and their faeces at four other locations across the country since December 7, it said.
South Korea on Friday confirmed the outbreak of bird flu and more than 100,000 birds have been slaughtered as authorities seek to contain its spread.
Two poultry farms, one in the central city of Cheonan and the other in the southwestern city of Iksan, were confirmed to have been contaminated, the ministry said.
Health authorities placed a quarantine zone over a 10 kilometre (6.25 mile) radius, restricting movements of vehicles and people and carrying out emergency disinfection.
They have also stepped up inspections of wild birds and urged poultry businesses to take extra precautions such as erecting nets around their farms to keep wild birds out.
The avian influenza outbreak is likely to further strain the country's health system, which has already been struggling to contain swine flu and foot-and-mouth disease (FMD) cases across the country.
South Korea has been hit by avian influenza three times, with the last outbreak in April 2008.
In 2008, South Korea had to cull more than eight million birds to curb the virus, resulting in damages estimated at 200 billion won (194 million dollars at the time).
Four people were confirmed to have been infected with the bird flu virus in late 2003 in South Korea but they showed few symptoms, health authorities said.
Lethal bird flu strain confirmed in S.Korea wild duck