SEOUL (Reuters) - South Korea said on Saturday a poultry farm was hit by bird flu, saying it found the H5N1 strain of avian influenza in the country´s first outbreak in three years of the virus that is potentially fatal for humans.

The agriculture ministry said earlier this week it suspected that a highly virulent strain of bird flu killed 6,000 chickens at a farm in the southwest part of the country that lies on a path for migratory birds.

"It is the H5N1 strain," the agriculture ministry official said by telephone of test results. It was too early to say whether the strain found at the farm was highly pathogenic, he added.

The virus´ virulence could be known later on Saturday, he said

The remaining 6,000 or so poultry at the farm in North Cholla province have been culled, South Korean news reports said.

Between December 2003 and March 2004, about 400,000 poultry at South Korean farms were infected by bird flu.

During that outbreak, the country culled 5.3 million birds and spent about 1.5 trillion won to prevent the disease spreading, officials said.

Subsequent testing in the United States indicated at least nine South Korean workers involved in the mass cull had been infected with the H5N1 virus, but none of them developed any major illnesses, South Korean health officials have said.

Since the virus re-emerged in Asia in 2003, outbreaks have been confirmed in around 50 countries and territories, according to data from the World Organization for Animal Health.

North Korea had an outbreak of bird flu at poultry farms near the capital, Pyongyang, in February 2005, which caused it to cull more than 200,000 chickens and vaccinate 1.1 million poultry.

The World Health Organization said that as of November 13, there had been 258 cases of human infection of the H5N1 strain since 2003, killing 153 people. Many of the victims were Asians, with 98 deaths in Vietnam and Indonesia, WHO said.