North Korea’s unprecedented barrage of missiles is underscoring the cost of Washington’s tensions with Beijing, since China has shown little appetite for additional sanctions over the country’s nuclear program.

China, along with Russia, played a critical role in approving United Nations sanctions on their neighbor after Kim Jong Un tested an atomic bomb and launched a missile designed to carry warheads to the U.S. five years ago. There’s little prospect of finding such unity on the U.N. Security Council now, even though North Korea has fired about 100 ballistic missiles since the U.N. approved its last penalties in 2017.

The Biden administration has shown increasing frustration with China, which has long been North Korea’s most important benefactor. And the stakes are rising because the U.S. and its allies believe Kim’s regime is preparing to detonate a nuclear bomb for the first time in five years.