The huge mass of troops is expected to descend on Kursk, which Ukraine has had a foothold in for three months, in the coming days, Ukrainian officials believe.

Those soldiers would be joining the already 11,000 North Korean soldiers in the region. Ukrainian President Volodymyr Zelensky said on Thursday that some of these troops “have already taken part in hostilities against the Ukrainian military.”

According to U.S. officials, the Ukrainians will be hard to completely move from the region, and Russian and North Korean forces will most likely suffer significant casualties in the event of a larger attack. The North Korean troops, while outfitted with Russian uniforms and weaponry to blend in, will also be fighting as light infantry and will not have the advantage of armored vehicles, leaving them largely exposed to the drone attacks and artillery fire that have dominated the conflict.

Russia has been increasing its drone attacks on Ukraine, with Zelensky warning that Moscow was firing nearly 10 times more drones than did in the fall of 2023. These have included decoy drones that do not have lethal warheads, which are being mixed in in order to confuse Ukraine’s air defense systems.

The news of the impending large-scale attack on the Kursk region follows President-elect Donald Trump’s separate phone calls with Zelensky and Russian President Vladimir Putin this past week. Trump has claimed he would end the war on the first day of his administration.