South Korea's government said Thursday "effective and phased" measures will be taken over North Korea's dispatch of troops to fight for Russia against Ukraine, after the nation's spy agency confirmed that the North's soldiers have entered combat in Russia's Kursk.

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, who were previously sent to Russia, are now in Kursk Oblast and are "already engaging in combat" operations against Ukraine. Source: Yonhap, citing South Korea's spy agency Details: The intelligence service reported that "North Korean soldiers dispatched to Russia have moved to Kursk Oblast over the past two weeks and their deployment to battlefields has been completed".