Mr Kim highly praised the 7th Infantry Division's 'militant training spirit and set forth the tasks for increasing its combat ability in every way,' the communist state's official news agency reported. It did not say when the visit was made.

The report came one day after Pyongyang vowed to build more nuclear bombs and start enriching uranium for a new atomic weapons programme after the Security Council imposed sanctions for its May 25 nuclear test.

US Secretary of State Hillary Clinton said Washington would do all it could to prevent continued proliferation by the North. 'The North Koreans' continuing provocative actions are deeply regrettable,' she told reporters Saturday during a visit to Canada.

The North Koreans, Mrs Clinton said, 'have now been denounced by everyone. They have become further isolated. And it is not in the interests of the people of North Korea for that kind of isolation to continue.' The 15-member Council voted unanimously Friday to slap tougher sanctions on the North to cripple its nuclear and ballistic missile programmes.

The North, in an angry response on Saturday, said all new plutonium it extracts would be used to make weapons. One third of used fuel rods from the Yongbyon reactor have so far been reprocessed into weapons-grade plutonium, it said.

'Secondly, we will start uranium enrichment,' it said in its first admission that it has such a programme - a second route to a nuclear bomb. In 2002, the North denied US claims that it was operating a secret uranium enrichment programme in addition to its admitted plutonium-based operation.

The plutonium-producing plants were shut down under a 2007 six-nation disarmament deal. But Pyongyang vowed to restart them after the Security Council in April condemned its long-range rocket launch.

'It has become an absolutely impossible option for the DPRK (North Korea) to even think about giving up its nuclear weapons,' the statement said, adding that any attempted blockade would be considered an act of war 'and met with a decisive military response.'

The North last year reported that it had extracted 30 kilogrammes (66 pounds) of plutonium from its Yongbyon complex over the years. It is not known whether this has already been weaponised. It could produce an additional six kilos by reprocessing 8,000 spent fuel rods, Professor Yang Moo-Jin, of Seoul's University of North Korean Studies said, giving it access to 36 kilos - enough for eight or nine bombs. -- AFP