SEOUL: The United States and its ally South Korea have drawn up a contingency plan to cope with emergencies in North Korea, including a possible regime change there, a report said Sunday.

"Operational Plan (OPLAN) 5029" was completed by Seoul and Washington recently, Yonhap news agency said, quoting an unnamed Seoul source.

It dictates how to respond case-by-case to such emergencies in North Korea as a civil war, an outflow of weapons of mass destruction (WMDs), a mass influx of refugees or a natural disaster, Yonhap said.

Under the plan, the United States assumes the role of eliminating North Korea's WMDs, including its nuclear weapons, while South Korean troops play a leading role in most other parts, it said.

Officials at Seoul's defence ministry were not immediately available for comment on the report.

North Korea has strongly protested at US-South Korean discussions of contingency plans which it denounces as preparations to invade the communist state.

Such discussions had been suspended under the previous liberal Seoul government which feared such a plan could infringe on its own sovereignty.

Yonhap said the discussions resumed after conservative President Lee Myung-Bak took office last year, with the plan completed recently.

"If South Korean-US combined forces intervene in North Korea's internal instabilities, the South Korean military will mostly assume the leading role in consideration of neighbouring countries," the source told Yonhap.

"But the US military will be responsible for the removal of the North's nuclear facilities and weapons."

Both sides are concerned about a possible transfer of the North's WMDs and relevant technology to terrorist groups or other countries, the source said.

The source added South Korea and the US would continue to complement and develop specific details of the contingency plan.

The two Koreas remain technically at war after the 1950-1953 Korean conflict ended in a fragile armistice rather than a peace treaty.

The United States stations some 28,500 troops to bolster South Korea's 655,000-strong armed forces against North Korea's 1.2 million-member military.