SEOUL, South Korea - South Korea said Monday it has lifted all special restrictions imposed to prevent the spread of bird flu after a series of recent outbreaks.

The Agriculture Ministry said in a statement it has slaughtered about 8.5 million birds to combat outbreaks of the disease that began in early April.

However, the ministry said no new outbreak has been found since May 12, and that as of Sunday it has lifted all special quarantine measures, such as restrictions on the movement and sale of poultry.

South Korea hopes to proclaim itself free of the disease in mid-August and report it to the World Organization for Animal Health, according to the ministry. Under the organization"e;s regulations, a country can officially declare itself free of the disease if no new cases of bird flu have been found for three months.

Bird flu hit South Korea in 2003 and 2006, resulting in the killing of millions of chickens, ducks and other poultry.

The ministry said it suspected this year"e;s bird flu outbreak was caused by migratory birds or foreign workers and tourists who visited China or Vietnam.

The virus remains hard for people to catch, but scientists worry it could mutate into a form that spreads more easily between humans, with the potential to kill millions worldwide. South Korea has reported no human infections of the H5N1 strain of bird flu that has killed 243 people elsewhere in the world, according to the World Health Organization.