Thousands of chickens in North Korea died from bird flu (search) at a processing plant last month, according to a news report Tuesday.

North Korea (search) is believed to be preparing emergency measures following the outbreak of avian influenza at the chicken plant in the North's capital city of Pyongyang, an unnamed source familiar with North Korea told South Korea's Yonhap news agency.

The facility is believed to be one of the biggest chicken factories in North Korea, according to the source who spoke with North Korean officials traveling in China (search). He added that it wasn't clear if that was the only affected site.

The report did not say what test was performed to verify the presence of bird flu or if the virus was the H5N1 strain, which has proven to be deadly to humans.

South Korean officials weren't immediately available for comment.

North Korea's state media announced last year that the country was strengthening quarantine measures against bird flu following the outbreak of the virus in Southeast Asian countries, but there haven't been any previous reports of the virus in North Korea.

Bird flu has killed 33 people in Vietnam, 13 of them in the latest outbreak that began in December. A Cambodian woman died earlier this year; Thailand has had 12 deaths.

South Korean officials said Monday that a South Korean trading company had delayed plans to import 40 tons of poultry from North Korea, but did not give a reason.