The United States' point man on North Korea arrived in Seoul Tuesday, calling for "serious negotiations" to ease tensions over Pyongyang's nuclear programme and deadly attack on a South Korean island.

Ambassador Stephen Bosworth, the US special representative for North Korea policy, said he would closely coordinate with South Korea and China on how to deal with Pyongyang.

"We believe that serious negotiations must be at the heart of any strategy for dealing with North Korea and we look forward to being able to launch those at a reasonably early time," he told reporters at the airport.

China has proposed bringing together the envoys of long-stalled six-nation disarmament talks on the nuclear-armed North to defuse tensions.

But Seoul, Washington and Tokyo have been lukewarm to the idea, saying Pyongyang first needs to show it is sincere about denuclearisation and mending ties with Seoul.

"I will let the Chinese speak for themselves on that. I think, by and large, we've been working together with them very effectively. That's an important relationship for both countries," Bosworth said.

The envoy is scheduled to meet his South Korean counterpart, Wiung-Lac, and Foreign Minister Kim Sung-Hwan Wednesday before flying to Beijing.

Cross-border tensions have been high since the North shelled a South Korean island on November 23, killing four people including two civilians.

The North also raised security fears that month by disclosing a uranium enrichment plant to visiting US experts.

It has insisted the plant is designed solely to fuel a light-water reactor being built to produce energy. But US officials and experts say this could easily be converted to produce weapons-grade uranium.

The North shut down its ageing plutonium-producing reactor in 2007 under a deal agreed with the six-nation negotiating group -- which also includes Russia.

But it quit the forum in April 2009 and staged a nuclear test a month later, its second since 2006.

Bosworth's Asia tour, which also takes in Tokyo, comes after Seoul reached out to Pyongyang with a signal to open talks after months of high tensions.

North Korea, in a joint New Year editorial by state media on Saturday, said tensions "should be defused as early as possible," stressing dialogue, and that cooperation "should be promoted proactively."

In an apparent response to the North's conciliatory gesture, South Korean President Lee Myung-Bak said Monday that Seoul was open to talks if Pyongyang showed its sincerity towards mending ties.

At a briefing in Beijing, China's foreign ministry spokesman Hong Lei also called for a resumption of the six-party talks, saying that "the current situation on the Korean peninsula remains complicated and sensitive.

"We call on relevant parties to adopt a responsible attitude... and push for the situation to come back to the track of dialogue and consultations as soon as possible," he said.

" China will continue as always to play a constructive role on this. The six-party talks are the effective way to realise denuclearisation on the Korean peninsula and maintain regional peace and stability."

In Tokyo Japanese Foreign Minister Seiji Maehara Tuesday said his government is open to direct talks with North Korea this year.

"We want to create an environment that will make it possible for us to further strengthen (efforts) to hold direct dialogue this year, and not only in multilateral settings," Maehara told a briefing.

The defence chiefs of South Korea and Japan will hold talks in Seoul next week to discuss increasing military cooperation and how to tackle the North.

Since North Korea's shelling of Yeongpyeong island, the South has staged a series of military exercises, including a live-fire drill on December 20 on the outpost, but Pyongyang did not follow through with threats to respond.

South Korean marines and naval forces will hold joint war games this week to simulate an infiltration by North Korean troops.

Rodong Sinmun, the North's communist party daily newspaper said Tuesday that such exercises demonstrated Seoul's "persistent design for invasion".

"They are advised to behave themselves, mindful that confrontation and war will bring earlier their own doom," it said.