The U.S. says there will be a "firm response" as Ukrainian forces holding ground in Russia's Kursk region now face North Korean troops "engaging in combat."

Ukrainian officials expect a counteroffensive in western Russia to begin in the coming days as North Korea’s troops train with Russian forces.

North Korean troops are experiencing numerous “difficulties” fighting for Russia in Ukraine, according to British intelligence. Pyongyang has sent around 10,000 fighters to the region as part of a military co-operation agreement with Kiev, the Ministry of Defence said in its latest update on the war.