That proximity has irked China, North Korea’s main backer. Chinese officials fear that Russia’s influence over the insular dictatorship is growing at China’s expense. They also worry that the United States and its allies in Europe and Asia will strengthen military cooperation in response to Russia and North Korea’s newfound closeness.

Amid reports that Pyongyang’s troops are on the front lines, speculation is rampant among Ukrainian troops about when the first large-scale clashes will happen.