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."

Experts tell Andy Gregory and Tom Watling that the real question is how much Kyiv’s troops are able to inflict casualties on the Russians as the price for taking the territory back

Russia attacked the Ukrainian capital Kyiv with a sophisticated combination of missiles and drones for the first time in 73 days on Wednesday, authorities reported, as the Pentagon said most of the North Korean troops sent to help Moscow’s war effort are fighting to drive Ukraine’s army off Russian soil in the Kursk border region.

The reconsolidated 47th Mechanized Brigade, its people and vehicles no longer scattered across a wide front in western Russia, is directly in the Russians’ crosshairs in Kursk. On Tuesday, 30 Russian vehicles barreled toward the 47th Mechanized Brigade in five waves.

The recent Russian counterattacks in Kursk have retaken up to half of the territory first seized, casting doubt on how long Kyiv will be able to continue holding it.

The video shows soldiers from Ukraine’s 36th Separate Marine Brigade targeting Russian troops and military equipment, including tanks and armored vehicles. Read also: Ukrainian forces detail enemy's failed assaults in Kursk Oblast "Russian generals send their elite soldiers to slaughter.