Ukraine has lost more than 40% of territory in Kursk Oblast, which quickly took over in a surprise invasion in August as Russian forces mounted waves of counterattacks, said a senior Ukrainian military source quoted by "Reuters".
The source, who is with Ukraine's General Staff, said Russia has deployed about 59,000 troops in Kursk Oblast since Kiev's forces invaded.
"We controlled about 1,376 square kilometers, now, of course, this territory is smaller. The enemy is increasing its counterattacks," the source said.
"We now control approximately 800 square kilometers. We will hold this territory as long as is militarily appropriate."
The Kursk Offensive was the first land invasion of Russia by a foreign power since World War II and caught Moscow off guard.
With the Kursk invasion, Kiev aimed to halt Russian attacks in eastern and northeastern Ukraine, force Russia to gradually withdraw its advancing forces in the east, and give Kiev additional leverage in any future peace negotiations.
But Russian forces are still steadily advancing in Ukraine's eastern Donetsk region.
The Ukrainian General Staff source reiterated that around 11,000 North Korean troops have arrived in the Kursk region in support of Russia, but the bulk of their forces are still finalizing their training.
Moscow neither confirmed nor denied the presence of North Korean forces in Kursk.
The commander-in-chief of Ukraine's armed forces said on November 11 that its beleaguered forces were not only fighting fragile Russian reinforcements in Kursk, but were also struggling to reinforce two besieged fronts in eastern Ukraine and were preparing for an infantry assault in the south.< /p>
The General Staff source said the Kurakhovo area was the most threatened, as Russian forces were advancing there at 200-300 meters a day and had managed to break into some areas with armored vehicles backed by anti-drone defenses.
The city of Kurakhovo is a springboard to the critical logistics center Pokrovsk in the Donetsk region.
In total, Russia has about 575,000 troops fighting in Ukraine right now, a source at the Ukrainian General Staff said, and is looking to increase its strength to about 690,000.
Russia does not disclose the number of its soldiers in combat and these numbers cannot be independently verified.