Korean officials said Tuesday some 6 million ducks and chickens have been slaughtered since the spread of bird flu in this capital city.

The agriculture ministry said that this year is the worst bird flu outbreak to hit the city.

Bird flu was first reported in eastern Seoul at a small aviary run by Gwangjin district officials, the ministry said. Four birds there tested positive for the disease.

The ministry official said the outbreak was believed has been caused by infected pheasants in Seongnam city, south of the capital, where government officials purchased an infected bird at an open market.