(CNN) -- New documents posted on the websites of the Guardian and The New York Times suggest Chinese officials are losing patience with long-time ally North Korea. Senior figures in Beijing have even described the regime in the North as behaving like a "spoiled child."

According to cables obtained by WikiLeaks, South Korea's then vice foreign minister, Chun Yung-woo, said earlier this year that senior Chinese officials (whose names are redacted in the cables) had told him they believed Korea should be reunified under Seoul's control, and that this view was gaining ground with the leadership in Beijing.

Chun was quoted at length in a cable sent by the U.S. ambassador in Seoul, Kathleen Stephens, earlier this year. He is reported as saying that "the North had already collapsed economically and would collapse politically two to three years after the death of (leader) Kim Jong-il."

CNN has viewed the cables posted on the newspapers' websites and on the WikiLeaks website.

Chun, who has since become South Korea's National Security Adviser, dismissed the prospect of China's military intervention in the event of a North Korean collapse, noting that "China's strategic economic interests now lie with the United States, Japan, and South Korea -- not North Korea."

He said that younger generation Chinese Communist party leaders no longer regarded North Korea as a useful or reliable ally and would not risk renewed armed conflict on the peninsula, according to a secret cable to Washington.

In a separate cable from January this year, then-South Korean Foreign Mnister Yu Myung-Hwan is quoted as telling U.S. diplomats that "the North Korean leader [Kim Jong Il] needed both Chinese economic aid and political support to stabilize an 'increasingly chaotic' situation at home."

The cables suggest China is frustrated in its relationship with Pyongyang. One from April 2009 quoted Chinese Vice Foreign Minister He Yafei as saying that "North Korea wanted to engage directly with the United States and was therefore acting like a "spoiled child" in order to get the attention of the "adult." The cable continued: "China therefore encouraged the United States, 'after some time,' to start to re-engage the DPRK."

In October 2009, a cable sent from Beijing recounted a meeting between U.S. diplomats and Chinese State Councillor Dai Bingguo, who had recently met Kim Jong Il. According to the leaked cable, Dai noted that Kim had lost weight when compared to when he last saw him three years earlier, but that Kim appeared to be in reasonably good health and still had a "sharp mind."

Dai also spoke about Kim's liking for alcohol. The cable continued: "Kim Jong-il had a reputation among the Chinese for being 'quite a good drinker,' and, Dai said, he had asked Kim if he still drank alcohol. Kim said yes."

The North Koreans told Dai that they wanted to have dialogue with the United States first and that they would consider next steps, including possible multilateral talks, depending on their conversation with the United States. North Korea held "great expectations for the United States," said Dai.

Further evidence of China's unease at Pyongyang's behavior came in a cable in June 2009 from the U.S. ambassador to Kazakhstan, Richard Hoagland. He reported that the Chinese envoy there was "genuinely concerned by North Korea's recent nuclear missile tests," and saw its nuclear activity a 'threat to the whole world's security.'" Hoagland reported that China's objectives were "to ensure they [North Korean leaders] honor their commitments on non-proliferation, maintain stability, and 'don't drive [Kim Jong-il] mad.'"

It seems the Russians were similarly frustrated by North Korean obduracy. In April 2009, a U.S. diplomatic cable quoted a senior Russian official as saying that "Foreign Minister Lavrov had a difficult trip to North Korea that did not reveal any flexibility in DPRK's position." The Russian official assessed that Pyongyang was "hunkering down for a succession crisis."