Moscow’s forces are three miles from Dnipropetrovsk, a province they have never invaded. If they cross in, the advance would be a morale blow to Ukraine and complicate any territorial negotiations.

North Korea has deployed thousands of troops to support Russian forces fighting in Ukraine, according to Ukrainian, U.S. and South Korean assessments, Pyongyang's first major involvement in a war since the 1950s.

North Korean security services are telling their troops stationed in Russia's Kursk Oblast that they are fighting against both the Ukrainian and South Korean militaries, South Korean newspaper Chosun Daily reported,