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."

On the night of November 13, Russia launched a large-scale air attack on Ukraine, using various types of missiles, guided bombs, and attack drones. According to the Ukrainian Air Force, 96 Russian air targets were recorded.

Also on Monday, the Kremlin denied that President-elect Trump spoke with Russian leader Vladimir Putin last week.