China has been refusing to supply North Korea with special fuels needed for the North Korean armed forces and weapons development programs. China is  major source for petroleum products used by North Korea, and provides the fuel either free, as foreign aid, or at low prices. China has also been trying to convince North Korea to reform it's economy, like China has done, and stop developing nuclear weapons. North Korea has been trying some economic reforms, but the North Korean economy is in much worse shape than China's ever was, and the reforms have been haphazard so far. North Korea has steadfastly refused to stop its ballistic missile and nuclear weapons programs. The Chinese are getting more upset about how the North Korean leadership is mismanaging things. China is applying more pressure to North Korea, and has apparently got the U.S. to go along with any deal the Chinese diplomats can extract from the northerners. What the North Korean leaders want is to stay in power, and they want the United States to provide food and oil to make that happen, as well as a promise to not invade. As cocky as the northern leaders sound in their propaganda, privately, they were horrified at how quickly the American armed forces toppled Saddam Hussein. The North Korean communists feel they have their population brainwashed more thoroughly than Saddam had his, but they also note increasing unrest in North Korea. They do not want to risk the results of an American invasion, and are willing to consider regular inspections to insure that an agreement to halt missile and nuclear weapons development is being adhered to. This is what the U.S. insists on before it will agree to provide aid and an "assurance" that there will be no invasion. The North Koreans are bargaining from a position of weakness and paranoia, so these negotiations drag on, and on.