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."

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,

North Korean soldiers deployed to the Kursk region of Russia have begun combat operations against Ukrainian troops, the U.S. State Department confirmed Tuesday.