For more than five years, China has been a major player in the six-party talks aimed at persuading North Korea to give up its nuclear weapons program.

The conventional wisdom is that China is North Korea's staunchest ally and greatest source of support in the international community.

Economically, Beijing is Pyongyang's major supplier of food and energy. Roughly 80 percent of consumer goods found in North Korea are made in China. Beijing is interested in North Korea's raw materials such as coal, iron ore and limestone as well as its precious metals such as gold.

Diplomatically, for the past several years, China has been the host of the six-party talks bringing together in addition to Beijing, the United States, Russia, Japan, South Korea and North Korea.

The aim of these negotiations is to persuade Pyongyang to eliminate its nuclear weapons capabilities. However, North Korea has withdrawn from those talks after strong international criticism of its recent [April 5th] test launch of a long range ballistic missile.

Analysts say despite strong political, economic and historical ties, the relationship between China and North Korea is far from cordial. One of those analysts is James Walsh, nuclear and security expert at the Massachusetts Institute of Technology [MIT, Cambridge, Mass.] who has traveled to North Korea on several occasions. "It has been a rocky relationship. Because North Korea, on the one hand, feels emotional ties to China, but on the other hand is scared to death that China, a great power, is going to overwhelm it economically - or worse, cut a deal with the Americans, leaving it out in the cold. So North Korea is of two minds when it comes to China: it welcomes China's support, but is also fearful. It is fearful of the great powers, it's fearful that it's going to be stomped on when these giants - United States, China, Japan - are making their back room [ie. secret] deals. That's what North Korean officials tell me," he says.

Analysts say there is a lot of debate as to how much leverage China can exert on North Korea and whether Beijing could persuade Pyongyang to rejoin the six-party talks.

Drew Thompson is a China expert with the Nixon Center, a non partisan, public policy institution. "China definitely has influence and it has leverage. Often U.S. officials have stated that China is not using all of its leverage. And sometimes that simply refers to China's essential delivery of aid shipments, of food and energy, whereas the U.S. officials have stated in the past that if China would just turn off the oil and energy going into North Korea, then North Korea would have to respond. The Chinese are very reluctant to use that opportunity to really apply coercive pressure on North Korea because they believe that North Korea would not respond kindly and it would basically ruin or undermine the existing China-North Korea relationship and take away the ability that China currently has to communicate with Pyongyang fairly effectively. So China does have leverage, but they also, at the same time, feel a little bit helpless," he says.

David Kay is the former chief nuclear weapons inspector for the International Atomic Energy Agency. He also believes China has leverage over North Korea - but he says it is hard to use. "Theoretically, the Chinese could tap down on [reduce] their fuel and food supplies to North Korea. But the Chinese will tell you - and I think it's a legitimate response - that look, what they're afraid of is a rapid collapse in North Korea, which would lead to an influx of Koreans into Manchuria across the Yalu River, destabilizing that area. So they are reluctant to use the power they have - but they have far more influence than anyone else with North Korea," he says.

Drew Thompson from the Nixon Center says China would prefer to have a stable and economically viable North Korea on its border. "The Chinese preference for North Korean future scenarios would very much look like a smaller model of China, or China's north-east region, with privatization and slow, incremental reform of the economic sectors and gradual opening of social rights and freedoms for individual citizens - but maintaining its authoritarian political structure, very much as China has done over the last 30 years. And I think there's a great deal of frustration that North Korea has not followed that Chinese model for economic reform," he says.

Regarding the six-party talks on North Korea's nuclear weapons program, Thompson and others say China does have some leverage over North Korea. Analysts say if anyone can persuade Pyongyang to go back to the negotiating table, it is Beijing. But experts also say the Chinese government must figure out how much pressure it can exert and how far it can push before instability is triggered in North Korea, bringing about  potentially, an even greater crisis.