Years of failed efforts to stem North Korea's nuclear and missile programs have followed a usual pattern. If enforced, the loss of coal revenue could tighten the screws on leader Kim Jong Un after his government's acceleration of nuclear and missile tests this last year. "If China is squeezing North Korea, it is for one purpose and one purpose only: to offer a cooperative gesture to the incoming Trump administration in return for an initiative on negotiations," said Stephan Haggard, a North Korea expert at the University of California, San Diego. Foreign Ministry spokesman Geng Shuang said the country wants parallel negotiations on nuclear matters and a formal peace treaty to replace the armistice ending the 1950-53 Korean War — a longstanding North Korean request. Kim has shown little interest in relinquishing his nation's nuclear deterrent as he closes in on a weapon capable of targeting mainland America, and Sino-American disputes over the best approach to dealing with the confounding North Korean leader have hamstrung international diplomatic efforts. These could include embarrassment over the apparent assassination of Kim Jong Nam, the North Korean leader's exiled, half-brother who was spending much of his time in China. While it opposes the North's pursuit of nuclear weapons, Beijing fears any policies that might lead to an influx of North Koreans into China or a U.S.-allied, unified Korea emerging on the Chinese border. A high-profile North Korean defector reported that Kim wants to finish an intercontinental ballistic missile capable of hitting the U.S.