Over 40% of the territory Ukraine seized in Russia's Kursk region during a surprise August incursion has been lost amid intensified Russian counterattacks, a senior Ukrainian military source told Reuters.

Ukrainian forces, which initially controlled 1,376 km², now hold approximately 800 km² as Russia reinforces its defenses with tens of thousands of troops, according to Reuters.

"At most, we controlled about 1,376 km² (531 mi²), now of course this territory is smaller. The enemy is increasing its counterattacks," the source said.

"Now we control approximately 800 km² (309 mi²). We will hold this territory for as long as is militarily appropriate."

Read more: Ukraine's military campaign 'derailed', forces 'ground down': Russia

This comes amid intensified combat along the frontlines as both Russia and Ukraine brace for potential shifts in US policy under the upcoming administration, which could significantly impact the course of the war.

Kursk was initially seized by Ukrainian forces in a surprise offensive in August, marking the first ground invasion of Russian territory by a foreign power since WWII.

Troop deployment

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According to the General Staff source, Russia has deployed approximately 59,000 troops to the Kursk region and currently has around 575,000 troops involved in the war, with plans to increase this number to 690,000.

The source further alleged that around 11,000 DPRK troops have reportedly arrived in the Kursk region to support Russia, though the majority of these forces are still in the process of completing their training.

With regards to challenges on other fronts, the source noted that Ukraine is simultaneously dealing with intense pressure on two besieged fronts in eastern Ukraine.

The situation is further complicated as Ukrainian troops brace for a potential infantry assault in the south, adding to the strain on their already stretched resources. 

Read more: Russia will respond in mirror-like fashion if Ukraine escalates: Putin

Kurakhove as a critical threat

The General Staff source identified Kurakhove as one of the most critical threats facing Ukrainian forces.

Russian troops in the region are advancing at a rate of 200 to 300 meters per day, employing armored vehicles and sophisticated anti-drone systems to breach Ukrainian defensive lines.

The source noted that Kurakhove's strategic location as a stepping stone toward the key logistical hub of Pokrovsk in the Donetsk region makes it a particularly vulnerable point in Ukraine's defenses.

In some areas, Russian forces have managed to break through Ukrainian lines with armored vehicles backed by anti-drone systems.

Reinforcement of Air Defenses

Finally, the source detailed that Ukrainian officials are reportedly in talks with the US and the UK about acquiring advanced air defense systems to safeguard Ukrainian cities and civilians against emerging longer-range aerial threats.

While Ukraine is bolstering air defenses over Kiev, similar measures are planned for Sumy and Kharkov, cities near the front lines.