North Korea's new uranium enrichment programme is designed to make nuclear weapons, South Korea's foreign minister has said, rebutting Pyongyang's claims that it is for peaceful use.

"I think it is part of an attempt to produce nuclear bombs on top of plutonium-based ones," Kim Sung-Hwan said in an interview with Yonhap News Agency published Thursday.

The North raised regional security fears last November by revealing an apparently operational uranium enrichment plant to visiting US experts.

It says the plant will fuel an experimental light water reactor now under construction to generate electricity.

But senior US and other officials fear it could easily be reconfigured to produce weapons-grade uranium to augment the country's existing plutonium stockpile.

The North quit six-party nuclear disarmament talks in April 2009 and conducted its second atomic weapons test a month later.

The forum, chaired by the North's major ally China, also includes the two Koreas, the United States, Japan and Russia.

Kim said efforts to revive the negotiations have recently gained momentum. He said Seoul, Tokyo and Washington have "considerably narrowed down opinions" with Moscow also "getting there to some degree".

"China has slightly different opinions on the North's stance so we have more to discuss (with Beijing)," the minister told Yonhap.

The North has indicated willingness in principle to return.

But the United States, Japan and South Korea say it must mend ties with the South and show seriousness about denuclearisation before discussions resume.

Cross-border ties have been icy since South Korea accused the North of mounting a torpedo attack on a warship, the Cheonan, last March with the loss of 46 lives. The North denies involvement in the sinking.

Tensions rose to their highest level for years when the North on November 23 shelled a South Korean border island, killing four people including civilians.

But in a change of tack this year, Pyongyang has been calling for dialogue.

Kim restated the South's conditions for any dialogue, saying the North must take responsibility for the attacks and show commitment to nuclear disarmament.

"There should be some sort of responsible measures about the Cheonan's sinking and the Yeonpyeong shelling. There should be a firm pledge that such provocations won't be repeated and we also have to first make sure (the North) is serious about denuclearisation," he told Yonhap.

earlier related report
N. Korea must take action to defuse tension: Gates
Tokyo (AFP) Jan 13, 2011 - US Defense Secretary Robert Gates Thursday urged North Korea to take concrete steps to show it is "serious" about talks after the nuclear-armed regime offered to resume dialogue after months of tension.

Gates, in Tokyo as part of an Asia tour, called on the regime to cease its "belligerent behaviour" and said that US efforts were focused on preventing Pyongyang from resorting to aggression.

Although the US supported reviving talks, "there must be concrete evidence on the part of the North that they are finally serious about these negotiations," Gates said at a news conference with his Japanese counterpart, Toshimi Kitazawa.

During an earlier stop in Beijing, Gates suggested North Korea could prove its sincerity by freezing further missile or nuclear tests.

Describing his talks in the region this week, the Pentagon chief said the United States, Japan, South Korea and China all had a "common interest" in securing peace and stability on the divided Korean peninsula.

Washington has worked with all four countries to try to prevent tensions in the region from spinning out of control after Pyongyang shelled a South Korean island in November, killing four people.

The United States has repeatedly pressed China to exercise its influence with its ally North Korea, and Gates this week credited Beijing with playing a helpful role.

The North quit six-party nuclear disarmament talks in April 2009 and conducted its second atomic weapons test a month later, but has indicated willingness to return to the talks.

The forum, chaired by the North's major ally China, also includes the two Koreas, the United States, Japan and Russia.

South Korean Foreign Minister Kim Sung-Hwan meanwhile said efforts to revive the negotiations had gained momentum.

"China has slightly different opinions on the North's stance so we have more to discuss (with Beijing)," the minister told Yonhap News Agency.

Despite Pyongyang's positive statements, the United States, Japan and South Korea say the North must mend ties with the South and show seriousness about denuclearisation before discussions resume.

Gates -- who will fly to Seoul on Friday -- warned earlier this week that North Korea had made progress with its long-range ballistic missile programme and that Pyongyang would pose a direct threat to the United States within five years.

Cross-border ties have been severely strained since South Korea accused the North of mounting a torpedo attack on a warship, the Cheonan, last March with the loss of 46 lives. The North denies involvement in the sinking.

Tensions rose to their highest level for years when the North on November 23 shelled South Korean border island.

The US and Japanese defence chiefs struck a positive tone on the thorny issue of relocating a US military base in Okinawa, with Gates saying the United States hoped to move forward while "reducing the impact on the communities nearby."

The allies reached an accord in May to move the US Marine Corps Futenma Air Station from an urban to a coastal area of Okinawa, but the Japanese government still faces domestic opposition to the plan from islanders, many of whom want the noisy air base off the island altogether.

The two also discussed Japan's plans for new fighter jets, with Gates suggesting Tokyo consider buying American aircraft, a US defence official said.

Kitazawa said his government was reviewing the possibility of providing a joint US-Japan sea-based missile shield system to other countries.

A bilateral accord now bars the export of the Standard Missile-3 ballistic missile interception system to other countries without Japan's contract.