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."

Russia has amassed a large force of tens of thousands — including recently arrived North Korean troops — to carry out an assault on the Ukrainian positions in Russia’s Kursk region expected in the coming days,

North Korean soldiers have engaged in combat operations against Ukraine alongside their Russian allies, South Korea's spy agency said on Wednesday. Seoul's confirmation comes amid growing global criticism as the two countries strengthen military ties,