North Korea has claimed it developed a poultry vaccine against the deadly H5N1 type of bird flu and is inoculating chickens as part of stepped-up efforts to prevent the disease following outbreaks in South Korea.

"The production of H5N1 vaccine locally developed recently in our country is increased and the compulsory vaccination of it to whole poultry flocks is being done," said Ri Kyong Gun, director of the North's Veterinary and Anti-Epidemic Department, in an interview with AP Television News in Pyongyang.

Ri did not say when the vaccine was developed or how effective it is.

Bird flu hit North Korea early last year, prompting the slaughter of about 210,000 chickens and other poultry. No new cases have since been reported.

Across the tightly sealed border with the South, three cases of bird flu have broken out since last month, forcing the government to cull more than 1.13 million poultry.

"Because of the bird flu outbreaks in South Korea recently, we are further strengthening quarantine efforts," Ri said.

At a chicken farm in Pyongyang on Wednesday, quarantine workers were disinfecting all trucks entering the farm, spraying disinfectants on the vehicles and putting disinfectant powder on the ground to make sure tires do not carry any virus, according to AP Television News video.

Quarantine workers at the farm were seen giving vaccine shots to chickens.

"Our chicken farm is taking thorough measures to ban contacts from outside, control vehicles and people coming in and out of the farm and vaccinate whole poultry flocks," said Jo Yong Pil, head of the farm's veterinary control team.