In a surprising move, China's commerce ministry has announced that the country would be suspending its coal imports from North Korea. China released a statement Saturday saying that the freeze in imports will begin Sunday and will be in place through the end of the year.The move marks a dramatic blow to North Korea. The country, which conducts an estimated 90 percent of its trade with China, relies on coal as its No. 1 export. In fact, as NPR's Elise Hu has reported, many analysts say coal makes for some 35 percent of North Korea's economy.China did not immediately state a reason for the coal freeze, though it comes at a turbulent time: Last week, Pyongyang test-fired a missile into the Sea of Japan, drawing international rebuke, and just days ago, North Korean dictator Kim Jong Un's older half brother died mysteriously in Malaysia — a death that has sparked speculation of assassination.It must be noted, this is not the first time China has made a move to comply with U.N. sanctions against the hermit kingdom. Last year, China also signed onto a resolution cutting off trade in coal and other commodities. But it also insisted on a "livelihood exemption," which "allows the export of a product if cutting it off might affect the livelihood of the exporter, so long as the revenue doesn't go to North Korea's nuclear program," Elise reported.It gave China a ready out, Troy Stangarone, senior director of congressional affairs and trade at the Korea Economic Institute, told Elise last year. The Chinese, who fear the prospect of a broken nuclear state on their eastern border, have long been North Korea's greatest supporter on the world stage."Right now the Chinese are essentially letting most of the trade go through," Stangarone said at the time. "This is one of the challenges — all of the sanctions, each country has to do their own implementation. By saying something is for a 'livelihood' purpose, it does give you enough wiggle room to say, 'Well, we can let this go through.' "With Saturday's announcement, however, that situation seems to be shifting.As a matter of fact, the shift to have have already begun: Citing South Korea's Yonhap news agency, Reuters reports a North Korean coal shipment — valued around $1 million — was rejected by China last week.It's "sign that Beijing's patience was running out" after the missile test and the death of Kim's half-brother Kim Jong Nam, according to The Washington Post. "If North Korea were responsible, it would be seen as an affront to Beijing, which had played host to and protected the half brother of the North Korean leader for many years." Copyright 2017 NPR. To see more, visit http://www.npr.org/.