Chinese officials are increasingly exasperated with close ally North Korea and some feel China's erratic neighbor is losing its strategic value for Beijing, according to leaked US documents.

The memos published by whistle-blower website WikiLeaks also allege that China may have turned a blind eye to illicit North Korean missile parts exports and that the top leadership was behind cyberattacks on Google and US targets.

Over an expansive dinner last year, the Chinese ambassador to Kazakhstan revealed that Beijing considers North Korea's nuclear program to be "very troublesome," according to one memo.

Ambassador Cheng Guoping "said China hopes for peaceful reunification in the long-term, but he expects the two countries to remain separate in the short-term," said the leaked cable by US Ambassador Richard Hoagland and reprinted by Britain's Guardian newspaper.

China has given a muted response to the leaks -- which have left key American allies red-faced by embarrassing revelations -- urging the United States to "properly handle" the issue.

"We hope the US side will properly handle relevant issues," foreign ministry spokesman Hong Lei said when asked about the leaks, adding that Beijing did not "want to see any disturbances to China-US relations."

In one cable reproduced by The New York Times, a Chinese official whose name was removed said Beijing believed North Korea had "gone too far" after carrying out its second nuclear test in 2009 and firing a missile.

The official told a US diplomat "that Chinese officials had expressed Chinese displeasure to North Korean counterparts and had pressed (North Korea) to return to the negotiation table," it said.

"Unfortunately," the Chinese official was quoted as saying, "those protests had had no effect."

"The only country that can make progress with the North Koreans is the United States," the official said, according to the cable.

WikiLeaks has outraged the US government with its massive release of sensitive data. The memos became public a week after North Korea shelled a South Korean border island, killing four people and sending tensions soaring.

China -- North Korea's main ally and economic lifeline -- has come under huge pressure to use its influence on Pyongyang to ease the situation, but so far, Beijing has refused to publicly condemn its neighbor.

The leaked documents suggest China has less influence on North Korea than is commonly thought and that the reclusive communist state may have lost some of its strategic value for Beijing.

Many US experts believe China wants to preserve the status quo on North Korea, fearing that a collapse would trigger a flood of refugees and bring a united and US-allied Korea to its border.

But senior South Korean official Chun Yung-Woo is quoted in a cable as saying that more "sophisticated" Chinese officials have come to believe that North Korea "has little value to China as a buffer state" since its first nuclear test in 2006.

Chun also said South Korea believed North Korea "had already collapsed economically" and would "collapse politically" two to three years after leader Kim Jong-Il's death.

Chun, who was then vice foreign minister and is now national security adviser, said China "had far less influence on North Korea than most people believe."

"Beijing had 'no will' to use its economic leverage to force a change in Pyongyang's policies and the (North Korean) leadership knows it," he said.

China has led six-nation talks on North Korea's nuclear program -- which also involve Japan, the two Koreas, Russia and the United States -- and Sunday proposed an emergency meeting.

But a cable showed dismissive views of some partners. One Chinese official was quoted as saying that South Korea has "plenty of ideas, but we've heard them all before."

The official also sharply criticized Japan, which has been pressing North Korea on the fate of citizens kidnapped in the 1970s and 1980s to train the regime's spies.

"Japan's obsession with the abductee issue reminded him of a Chinese expression for an individual who was too weak to make something work, yet strong enough to destroy it," the cable said.

The leaked documents also show frustration among US diplomats who pressed China in 2007 to block shipments of missile parts from North Korea to Iran via Beijing, the Guardian reported.

It was not known whether the demand led to action by Beijing, the report said.

In another cable, the US embassy in Beijing said it learned from "a Chinese contact" that the country's Politburo had led years of hacking into computers of the United States, its allies and Tibet's spiritual leader the Dalai Lama.

The New York Times said the embassy found that attacks against Google were "part of a coordinated campaign of computer sabotage carried out by government operatives, private security experts and Internet outlaws recruited by the Chinese government."