A highly pathogenic strain of bird flu was discovered in two dead cats on Saturday, a provincial government official said, marking the first infection of the virus found in mammals in two years.

The H5N6 strain of avian influenza (AI) which has infected chickens across the country was found in the bodies of the cats in Pocheon, some 46 kilometers north of Seoul, the official said, citing information from health authorities.

The cats were found dead earlier this week some 2 kilometers from a chicken farm where the strain of the virus was first reported last month.

It marked the first infection of AI in mammals in South Korea since February 2015 when the country reported the infection of bird flu in a dog.

Health authorities said that they are looking at samples to verify whether they were infected with a more highly pathogenic strain of AI.

"Even if it is the same N6 strain, there are some differences in gene structure," the official said. "We are awaiting test results."

South Korea is struggling to contain the spread of bird flu that has led to more than 20 million chickens and ducks nationwide being culled since mid-November.

(Yonhap)