South Korea's point man on North Korea warned Thursday of a global "nuclear domino effect" unless the communist state scraps its atomic weapons.

Unification Minister Hyun In-Taek was speaking days before senior US officials travel to South Korea, Japan and China for talks on the issue.

North Korea's atomic armament meant "major changes" in the region's security environment as well as the international order, Hyun, whose ministry handles cross-border relations, told a forum.

"It will produce nuclear domino effects across the globe," he said.

"Its nuclear programme is only pushing the North closer to a crisis," the minister added, saying that Pyongyang's weapons ambitions had "aggravated regime instability" and the impoverished country's economic woes.

The North bolted six-party nuclear disarmament negotiations in April last year following a United Nations reprimand for a long-range rocket test. It staged an atomic weapons test -- its second -- a month later.

China, which hosts the six-party forum that also including the two Koreas, the United States, Japan and Russia, is pushing to revive the dialogue.

But inter-Korean tensions remain high after the South accused the North of a deadly submarine attack on one of its warships.

At a separate event, the US military commander in South Korea said that the incident showed the North would focus on "asymmetric warfare" in any future provocations.

"We take the threat very seriously, what they will do in the future," General Walter Sharp, who commands 28,500 US troops in the country, told local reporters.

Given the strength of South Korean and US troops in a conventional all-out conflict, North Korea is "putting more money" into special operations forces, missile technology and nuclear weapons, Yonhap news agency quoted him as saying.

Sharp said annual US-South Korean war games staged last month practised a scenario that included stabilising the North following any conflict.

The computer-simulated exercise was based on lessons the US has learned from Iraq and Afghanistan, he was quoted as saying.

North Korea has reacted angrily in the past to such war planning, saying its real aim is forcible regime change.

The US envoy for North Korea, Stephen Bosworth, plus Sung Kim, the US special envoy for the six-party talks, and Daniel Russell, the National Security Council's Asia director, will make a three-country regional trip starting Sunday.

They will visit Seoul on September 12-14, Tokyo on September 14-15 and Beijing on September 15-16 as part of a flurry of recent consultations on the nuclear issue.

North Korea has reportedly finished preparing for a landmark meeting of its ruling communist party, and there is speculation it will confirm the youngest son of leader Kim Jong-Il as his eventual successor.

Secretary of State Hillary Clinton said Wednesday the United States was watching for any leadership changes but hoped that whoever is in power will scrap nuclear weapons.