SEOUL, Dec. 13 (Yonhap) -- South Korea quarantine officials have slaughtered more than 9.81 million poultry this winter, an official said Tuesday, the latest in a series of efforts to contain a bird flu that has ravaged chicken farms across the country.

They also plan to kill an additional 2.53 million chickens and ducks across the country in coming days, said Lee Yong-jin, deputy director handling the issue at the Ministry of Agriculture, Food and Rural Affairs.

That would raise to more than 12 million the total number of poultry culled since Nov. 16, when the first outbreak was reported at a chicken farm in Haenam, about 420 kilometers south of Seoul.

The outbreak -- the first in nearly seven months -- was caused by the highly pathogenic H5N6 strain of bird flu, a new type of virus that was first detected in South Korea.

In April, quarantine officials slaughtered 12,000 chickens and ducks.

The quarantine authorities said migratory birds are a source of the outbreak of bird flu as there have been no reports of infections through the movement of people or livestock.

South Korea culled 14 million birds in 2014.

South Korea has 155 million chickens and 8.7 million ducks as of the end of 2015.