SEOUL - Secretary of State Hillary Clinton arrives Wednesday in South Korea in a show of support for the close US ally as it confronts North Korea over a torpedoed warship.

The United States has promised unequivocal backing for the South, which has vowed to make the North pay following the attack which split a South Korean corvette in two in March with the loss of 46 sailors.

Clinton has been pressing Seoul's case in Beijing during two days of high-level meetings.

A multinational investigation concluded last week that the North carried out the attack, despite its denials. But China, unlike numerous other nations, failed publicly to criticise its ally and has called only for restraint.

As a veto-wielding UN Security Council member, China's support is crucial if South Korea is to secure the international punitive action it seeks.

China and the United States said Tuesday they would work together to resolve the crisis brewing in the Korean peninsula, agreeing that ensuring regional stability was crucial.

"We are ready to work together with the US and other parties and continue to stay in close touch on the situation on the Korean peninsula," Vice Foreign Minister Cui Tiankai told reporters.

Clinton said Washington and Beijing share the objective of peace and stability on the peninsula. "Now we must work together again to address the serious challenge provoked by the sinking of the South Korean ship."

In a sign of the problems ahead, North Korea said on Tuesday it was severing all ties with South Korea and cutting communications links in protest at being blamed for the sinking.

The North said it would expel all South Korean personnel from a jointly-run industrial estate at Kaesong north of the border, and ban South Korean ships and planes from its territorial waters and airspace.

Pyongyang accused South Korea's navy of trespassing in its waters and threatened military action.

South Korea has cut trade with its neighbour as part of a series of reprisals announced Monday, but is pinning hopes on a Security Council resolution and possible new sanctions to curb the North.

It pressed visiting senior Chinese official Wu Dawei on Tuesday to support international punitive efforts, apparently without result.

"The Chinese position still appears to be unclear," a foreign ministry official said.

President Lee Myung-Bak and Foreign Minister Yu Myung-Hwan will hope for a clearer readout of Beijing's intentions when they meet Clinton Wednesday.

The United States, which stations 28,500 troops in the South, has offered both military and diplomatic support in the standoff.

President Barack Obama Monday ordered his military chiefs to coordinate closely with Seoul "to ensure readiness and to deter future aggression".

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