South Korea and the U.S. have completed joint action plans to respond to a regime collapse and other internal emergency situations in North Korea, Yonhap News Agency reported Sunday, quoting a ranking government source.

The so-called "Operational Plan (OPLAN) 5029," drawn after years of bilateral consultation, dictates respective military responses by Seoul and Washington to several types of emergency situation in the communist North _ a civil war, an outflow of weapons of mass destruction (WMD), the kidnapping of South Korean citizens, a mass influx of refugees or a natural disaster, the source was quoted as saying.

Speaking on condition of anonymity, the source also noted that South Korea's military will play a leading role in enforcing OPLAN 5029, with the exception of the elimination of nuclear weapons and related facilities that will be handled by the U.S.

"South Korea and the U.S. had long worked on Concept Plan 5029 to prepare for a regime collapse and other internal emergencies in North Korea. Since its inauguration last year, the Lee Myung-bak government has pushed to convert the concept plan into an operational plan and it was recently completed," the source said.

"If the South Korea-U.S. combined forces intervene in North Korea's internal instabilities, the South Korean military will assume the leading role in consideration of neighboring countries, while the U.S. military will be responsible for the removal of the North's nuclear facilities and weapons."

He noted that South Korea and the U.S. will continue to complement and develop specific details of OPLAN 5029.

The two countries have expressed concern that the outbreak of an internal emergency in North Korea could lead to the transfer of its WMDs and relevant technologies to terrorist groups or other countries.