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,

According to assessments by the National Intelligence Service, North Korean forces deployed to Russia have moved to Kursk Oblast over the past two weeks,” intelligence officials noted. North Korean soldiers have now completed battlefield deployment and are actively engaged in combat.