Major powers expressed concern or alarm at North Korea's shelling of a South Korean island on Monday.

Among North Korea's neighbours, Russia said it saw a 'colossal danger' of an escalation in fighting on the Korean peninsula and China said it was imperative to resume six-party talks aimed at ending the North's nuclear weapons programme.

Following South Korean firing exercises near disputed waters, North Korea fired dozens of artillery shells at the island of Yeonpyeong. Two soldiers were killed and houses set ablaze in one of the heaviest bombardments of the South since the Korean War ended in 1953.

The United States urged North Korea to 'halt its belligerent action', saying that it was 'firmly committed to the defense of our ally, the Republic of Korea, and to the maintenance of regional peace and stability'.

The Pentagon said it was not reinforcing US forces stationed in the region but declined to say if it had raised their alert level.

Japan's chief cabinet secretary, Yoshito Sengoku, told a news conference that North Korea's action was 'unforgivable'.

A French diplomatic source said the UN Security Council could hold an emergency meeting in the next day or two.

'It is necessary to immediately end all strikes,' Russian Foreign Minister Sergei Lavrov told reporters during a visit to the Belarussian capital Minsk.

'There is a colossal danger which must be avoided. Tensions in the region are growing.'

China, the impoverished North's only powerful ally, was careful to avoid taking sides. 'It is imperative now to resume the six-party talks,' a spokesman for the Chinese Foreign Ministry told reporters.

The senior US envoy on North Korea, Stephen Bosworth, said after talks in Beijing that the United States and China 'both share a view that such conflict is very undesirable'.

China's economic and diplomatic support has been important to shoring up its otherwise isolated neighbour, whose leader Kim Jong-il has visited China twice this year to strengthen ties.

The NATO alliance, the European Union and Britain all condemned the North Korean attack, and Germany joined them in expressing concern and calling for restraint.

Analysts saw North Korea's action as a calculated tactic. They said it could be aimed both at boosting its leverage in international talks - an approach it has used in the past - and at reinforcing the domestic standing of the young heir apparent anointed by Kim Jong-il, his son Kim Jong-un.

'The shelling is likely succession-related in that the DPRK (North Korea) is seeking to build political capital for Kim Jong-un by attempting to enhance the perception of Jong-un's power base,' said Brittany Damora, analyst at the risk advisory firm AKE.

'In the North's view, Yeonpyeong is a great target in that it can strengthen the perception of its position without a real risk of counter-attack.'

Aidan Foster-Carter, senior research fellow at Leeds University, also said the recent introduction of Kim Jong-un onto the scene could be a factor. 'It might be him, it might be somebody doing it on his behalf. It could be different factions of the army.'

Alastair Newton, political analyst at Nomura in London, noted the South had made clear that it wanted to avoid an escalation, and said that the sinking of the South Korean warship Cheonan in March, although the North denied involvement, had arguably been more serious because of the 46 lives lost.

'Bottom line: together with possible preparations for a third nuclear test and the revelation at the weekend of the uranium enrichment facility, this looks like it could be North Korea playing hardball in anticipation of coming back to the negotiating table,' Newton said.

One European diplomat said it was conceivable that the attack could be an attempt by a faction in North Korea's secretive leadership to sabotage attempts at rapprochement with the outside world.

The political risk consultancy Stratfor said the attack was at odds with other recent North Korean actions, noting that Pyongyang had sent a list of delegates to Seoul for Red Cross talks due to take place on Thursday.

'With the ongoing leadership transition in North Korea, there have been rumours of discontent within the military, and the current actions may reflect miscommunications or worse within the North's command-and-control structure, or disagreements within the North Korean leadership,' it said.-Reuters