Image caption Chinese leaders are said to have grown increasingly frustrated with their North Korean allies

Officials in China have expressed frustration with communist ally North Korea, according to leaked classified US diplomatic cables.

Pyongyang was behaving like a "spoiled child", a Chinese foreign ministry official is quoted as having said in 2009, in cables released by Wikileaks.

Officials reportedly told South Korean counterparts that Beijing placed little value on the North as a buffer state.

The peninsula should be reunified under Seoul's control, they suggested.

The revelations come as regional tensions remain high after the North shelled a South Korean island a week ago.

The US administration says the Wikileaks disclosures are an attack on the world community, but that partnerships it had worked hard to build would withstand the challenge.

China has responded to the leaks by urging the US to "properly handle relevant issues," a foreign ministry official said on Tuesday.

'New reality'

One cable published on Monday reveals that China's Vice Foreign Minister, He Yafei, told the US charge d'affaires in Beijing that North Korea was behaving like a "spoiled child" to get Washington's attention in April 2009 by carrying out missile tests.

A second dispatch from September 2009 said Mr He had downplayed Chinese Premier Wen Jiabao's trip to Pyongyang, telling the US Deputy Secretary of State, James Steinberg: "We may not like them... [but] they are a neighbour."

He said Mr Wen would push for denuclearisation and a return to talks.

Six-party talks aimed at defusing the nuclear issue and involving the two Koreas, the US, China, Japan and Russia have been stalled since April 2009.

South Korea and the US say they should not resume until the North has made a genuine offer on halting its nuclear programme.

Another cable relays a discussion over an official lunch in February 2010 between former South Korean Vice Foreign Minister Chun Yung-woo and the US ambassador to Seoul, Kathleen Stephens.

The minister is said to have revealed that a new, younger generation of Chinese leaders no longer regarded North Korea as a useful or reliable ally, and would not risk renewed armed conflict on the peninsula.

Mr Chun confidently had predicted that North Korea "had already collapsed economically and would collapse politically two to three years after the death of Kim Jong-il", despite his efforts to obtain Chinese help and to secure the succession for his son, Ms Stephens wrote.

Analysis Many China-watchers are sceptical Beijing would accept a reunified Korea under the control of Seoul. It's clear from the cables some Chinese officials don't regard North Korea as a useful ally. But the suggestion the Chinese government would abandon Pyongyang is less credible, analysts say. The claim was made by a senior South Korean official during lunch with the US ambassador here - similar predictions were made before the demise of Kim Il-sung, Kim Jong-il's father. What these cables show is the lack of hard facts diplomats around the world have to go on when it comes to working out what's going on in North Korea. They're forced to rely instead on educated guesses that often turn out to be wrong.

"The PRC would be comfortable with a reunified Korea controlled by Seoul and anchored to the United States in a 'benign alliance' - as long as Korea was not hostile towards China," her message added.

While these cables offer fascinating insights, seasoned Korea-watchers caution that this is a very "South Korean" view of the policy debate in Beijing, says the BBC's diplomatic correspondent, Jonathan Marcus.

It remains unknown whether this South Korean assessment - as reported to Washington - is an accurate reflection of Beijing's current thinking, adds our correspondent.

Computer hacking

The communications between the US State Department and its embassies and consulates around the world were sent between 1966 and 2010.

Other revelations from despatches released on Tuesday include:

Afghan President Hamid Karzai freed dangerous detainees and pardoned suspected drug dealers because they were linked to powerful or historically significant figures

Former UK Prime Minister Gordon Brown proposed a deal with the US in which suspected computer hacker Gary McKinnon plead guilty in return for a guarantee that he serve his sentence in the UK

Former British Guantanamo Bay detainee Moazzam Begg was praised by US ambassador to Luxembourg Cynthia Stroum for his campaign to persuade European countries to take in remaining inmates. Mr Begg was arrested by the CIA in 2002 and released from Guantanamo in 2005. He was never charged with any offence

Wikileaks Website with a reputation for publishing sensitive material

Run by Julian Assange, an Australian with a background in computer network hacking

Released 77,000 secret US records of US military incidents about the war in Afghanistan and 400,000 similar documents on Iraq

Also posted video showing US helicopter killing 12 people - including two journalists - in Baghdad in 2007

Other controversial postings include screenshots of the e-mail inbox and address book of US vice-presidential candidate Sarah Palin Reaction to Wikileaks revelations What is Wikileaks? Where the cables came from Background to US embassy cables

Wikileaks has so far posted only 281 of the 251,287 messages it says it has obtained. However, all of the messages have been made available to five publications, including the New York Times and the UK's Guardian newspaper.

Wikileaks and the newspapers which have published the cables say they have done so in the public interest.

Aggressive steps were being taken against those who "stole" the information, said Secretary of State Hillary Clinton, adding that every country had to be able to have honest, private dialogue with other countries about issues of common concern.

No-one has been charged with passing them to Wikileaks, but suspicion has fallen on US Army Private Bradley Manning, an intelligence analyst arrested in Iraq in June and charged over an earlier leak of a classified video.

On Tuesday, Wikileaks said it was coming under cyber-attack for the second time in three days. The Distributed Denial of Service (DDoS) attack, as it is known, works by flooding a target with too much data for it to handle.

The cables release is the third mass Wikileaks release of classified documents; it published 77,000 secret US files on the Afghan conflict in July, and 400,000 documents about the Iraq war in October.

Wikileaks argues the release of the documents has shed light on the wars, including allegations of torture and reports that suggest 15,000 additional civilian deaths happened in Iraq.

Ecuador has offered Wikileaks founder Julian Assange "unconditional" residency in the country.

Deputy Foreign Minister Kintto Lucas praised people like Mr Assange "who are constantly investigating and trying to get light out of the dark corners of information".