China can only persuade and not pressure North Korea to cooperate, said Cui Yingjiu, a retired Beijing University professor and former Kim schoolmate. He runs a research center on North Korea.

"Kim Jong-Il doesn't listen to anybody. China has at times tried to force him to do this or that, but the results have not been good. It had the opposite effect," Cui told AFP in an interview.

"There's nothing China can do. It cannot interfere with North Korea's internal politics. It can only wait. It can only persuade."

US special envoy Joseph DeTrani was in Beijing this week pressing China to step up efforts to bring North Korea back to six-party talks over its nuclear weapons ambitions.

China is touted as the North's strongest ally, but Kim has long been trained to trust no one, not even its neighbor which fought on its side during the Korean War, Cui said.

He recalled a remark Kim made to him in the 1960s, when Beijing-Pyongyang were strong and both men were attending the Kim Il-Sung University in Pyongyang.

"He said his father Kim Il-Sung told him not to trust anyone, not Russia, not China," said Cui, an ethnic Korean who maintained contact with Kim until recent years and regularly received gifts from him.

Ideally Kim would wish to negotiate directly with the United States instead of through the six-party format, which has boosted China's influence.

"Kim prefers improving relations with the United States directly so that it can sideline China and play the US against China to its benefit as it played China and Russia against each other in the past," said Cui.

China's help, mostly in the form of fuel and food, is not as great as thought, Cui said.

Contrary to reports, Beijing, unlike Washington, does not support regime change, despite suggestions that it was harboring defecting generals from the North as a fallback plan in the event Kim lost control, he said.

"That could seriously jeopardise relations with the North, which will not be worth it. North Korea could begin developing relations with Taiwan," said Cui, who makes frequent trips to the North.

The Chinese leadership does not favor a sudden collapse of the regime, and would not open its doors to North Korean refugees despite recent US indications it would help deal with an influx.

Frustrated with Kim, Beijing still prefers to wait for him to change rather than prod him as Washington hopes, Cui said.

The greatest influence Beijing has had has been indirect -- simply serving as an example that a socialist regime can undergo economic reforms without losing its grip on power, Cui said.

Following Kim's trip to Beijing in 2000 which opened his eyes to the changes in China, he began experimenting with economic opening.

"He realized reform didn't necessarily lead to collapse," said Cui, who described Kim as outgoing and casual.

While resisting outside pressure, Kim will nevertheless cooperate with Washington, as he knows his food- and resource-deficient country has no other choice.

"They don't want to give up nuclear weapons, but they realize that if relations with the US remain frozen, nothing will work. It will not be able to get money from the World Bank, loans from Japan, or attract foreign investors," said Cui.

"So now they are simply waiting to see what the US can offer in terms of security guarantees or economic assistance."

The United States has refused bilateral talks and is insisting on a complete dismantlement of the North's nuclear program.

The six-way talks among the two Koreas, the United States, China, Japan and Russia, have been stalled since a third session in June. North Korea boycotted a fourth round scheduled for Beijing in September.