Russia prepares counteroffensive with 50,000 troops, potentially including North Koreans, sources say

LONDON -- As many as 50,000 Russian and North Korean troops are preparing to launch a new counteroffensive to push Ukrainian forces out of their positions in Russia's western Kursk region, multiple Ukrainian military sources told ABC News.

Moscow has been trying to push Ukrainian forces out of Kursk since they seized a chunk of the border region in a daring August offensive, marking the first time that Kyiv's forces have seized and held significant Russian territory since the full-scale invasion began in 2022.

The expected counteroffensive intends to retake land captured by Ukrainian forces in Kursk since August, Kyiv military sources told ABC News. North Korean forces will be involved, they said, but it is unclear how many of Pyongyang's soldiers are prepared to join the fight.

Pentagon spokesperson Maj. Gen. Pat Ryder said last week there are 10,000 North Korean soldiers deployed to Kursk.

"We'll see exactly how these forces are integrated into Russian operations, and how they're committed to the battlefield, assuming that they are replacements for Russian forces," Ryder told journalists during a briefing.

"Should these troops engage in combat support operations against Ukraine, they would become legitimate military targets," Ryder added.

Kyiv has used the Kursk operation to replenish its "exchange fund" of captured Russian soldiers, to bolster its negotiating position and to apply political pressure on the Kremlin. If renewed peace talks go ahead -- as President-elect Donald Trump has proposed -- occupied parts of Kursk could prove valuable bargaining chips for Kyiv.

Ukrainian President Volodymyr Zelenskyy said last month that the Kursk operation marked "a very important phase of the war," adding that Ukrainians "have proven that they can push the war into Russia."

Ukraine's top commander, Gen. Oleksandr Syrskiy, said in a Monday Telegram post that the importance of the Kursk operational area "cannot be underestimated given the number of enemy troops concentrated there."

"If it were not for the steadfastness of our soldiers, these tens of thousands of enemies from the best Russian shock units would have stormed our positions in the Pokrovsky, Kurakhiv or Toretsk directions, which would have significantly worsened the situation at the front," he added, referring to areas of intense fighting on the eastern front.

"Now, following the orders of their military leadership, they are trying to dislodge our troops and advance deep into the territory we control," Syrskiy said. "Our task in this direction is to deter and destroy the enemy on his land."

Ukraine's Kursk operation has not stopped Russian momentum in eastern Ukraine, where Moscow's troops have been reporting steady progress and the capture of villages, edging the front line westward.

ABC News' Will Gretsky, Patrick Reevell and Natalia Popova contributed to this report.