BEIJING -- Leaked U.S. diplomatic cables show China's frustration with communist ally North Korea and speculate Beijing would accept a future Korean peninsula unified under South Korean rule, according to the documents released by whistle-blowing website WikiLeaks.

The memos posted online by media organizations indicate the enormous import American and South Korean diplomats place on China's attitude toward the future survival of the isolated and impoverished hard-line communist regime in Pyongyang.

The release of the documents follows new tensions in the region with North Korea unleashing a fiery artillery barrage on a South Korean island that killed four people a week ago. The regime also warned that joint U.S.-South Korean naval drills this week had pushed the peninsula to the "brink of war."

China "would be comfortable with a reunified Korea controlled by Seoul and anchored to the US in a 'benign alliance' as long as Korea was not hostile towards China," then-South Korean vice-foreign minister, Chun Yung-woo, is quoted as telling U.S. ambassador to South Korea Kathleen Stephens in February.

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Chinese officials are also quoted as using mocking language in reference to North Korea, pointing to tensions between the two neighbors in contrast to official statements underscoring strong historical ties.

Then-Deputy Foreign Minister He Yafei is quoted as telling a U.S. official in April 2009 that Pyongyang was acting like a "spoiled child" by staging a missile test in an attempt to achieve its demand of bilateral talks with Washington.

China is also preparing to handle any outbreaks of unrest along its border with North Korea that could follow a collapse of the regime. Chinese officials say they could deal with up to 300,000 refugees but might have to seal the border to maintain order, the memos said, citing an unidentified representative of an international aid group.

The diplomatic cables warned, however, that China would not accept the presence of U.S. troops north of the demilitarized zone that currently forms the border between the two Koreas.

U.S. Secretary of State Hillary Rodham Clinton asserted Monday that WikiLeaks acted illegally in posting the material. Officials around the world have said the disclosure jeopardizes national security, diplomats, intelligence assets and relationships between foreign governments.

Britain's the Guardian newspaper and The New York Times were among five international media organizations to receive the documents in advance.

China has largely rebuffed calls to use its influence to force Pyongyang to moderate its behavior, while opposing harsh economic sanctions or international censure. Beijing has responded to the latest crises by repeating calls for a return to long-stalled, six-nation denuclearization talks that the North has rejected.