Seoul brushed off a threat of retaliation by Pyongyang to ban the entry of North Koreans linked to nuclear and other weapons programmes, saying it would faithfully fulfil its duties as a UN member.

Lee Jong-Seok, head of the ministry responsible for inter-Korean relations, said existing laws would allow the government to control or prevent entry by anyone the UN sanctions committee names as subject to travel restrictions.

He said Seoul was also tightening inspection of goods and materials shipped to North Korea, under the terms of the UN Security Council resolution imposed after Pyongyang's October 9 first ever atom bomb test.

"Once the sanctions committee designates persons or organizations (with links to WMD programmes), the government will control the country's trade, investment, financial payments and fund remittances" to those entities, Lee said.

The move came as visiting French President Jacques Chirac and President Hu Jintao of China, Pyongyang's closest ally, voiced "grave concern" at the test in a joint statement in Beijing.

"This is contrary to the goal of the denuclearization of the Korean peninsula and the efforts of the international community to strengthen the non-proliferation regime," they said.

Meanwhile a leading think-tank reported a growing crisis of hunger that it said was being overshadowed by the dispute over Pyongyang's weapons drive.

The International Crisis Group warned in a report that hunger was driving increasing numbers of North Koreans to risk their lives fleeing over the border to China, and urged Beijing to halt its policy of repatriating the refugees.

The humanitarian challenge was "playing out almost invisibly as the world focuses on North Korea's nuclear programme", the Brussels-based group said.

The ICG said China and South Korea were not putting maximum pressure on the North to scrap its nuclear programme because they feared a torrent of refugees if the economy collapsed.

But it warned that even without the UN sanctions, "the perfect storm may be brewing for a return to famine in the North."

The October 9 caused a global uproar with the UN Security Council issuing a resolution imposing economic sanctions aimed at reining in Pyongyang's weapons programme.

The North is believed to have secured up to 50 kilograms of plutonium, enough to make six or seven nuclear weapons, according to a South Korean defence ministry report leaked to the media.

The report, submitted to a meeting of top military commanders on October 10, a day after North Korea conducted its first nuclear test, said the communist state was now believed to be researching how to miniaturise warheads to fit them on missiles.

Separately, US Assistant Secretary of State Christopher Hill said North Korea had given no indication it would return to stalled six-party talks, one of the key planks of the UN resolution.

"The North Koreans haven't expressed an interest in having a dialogue with anyone really," Hill told reporters on the sidelines of a regional meeting in Fiji.

"We've made very clear that if they come back to the (six-party) process, we're certainly prepared to talk to them directly," he said, when asked about calls for Washington to engage in direct dialogue with Kim Jong-Il's regime.

North Korea pulled out of the six-nation talks in November last year in protest at financial sanctions imposed by Washington against Pyongyang for alleged money-laundering and counterfeiting.

Japan, meanwhile, said it would not lift its own sanctions on North Korea until the communist state clearly abandoned its nuclear programme.

Simply returning to multi-party negotiations was only a "starting point," Chief Cabinet Secretary Yasuhisa Shiozaki, the government spokesman.

North Korea "has to halt the nuclear development programmes in an evident way and respond to the voices of the international community over issues such as abductions."

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