When Kim Jong Un inherited power in North Korea in late 2011, then-Chinese President Hu Jintao was outwardly supportive of the untested young leader, predicting that "traditional friendly cooperation" between the countries would strengthen.

Two years later, Kim ordered the execution of his uncle Jang Song Thaek, the country's chief interlocutor with China and a relatively reform-minded official in the hermetic state.

Since then, ties between the allies have deteriorated so sharply that some diplomats and experts fear Beijing may become, like Washington, a target of its neighbor's ire.