Large group of Russian and North Korean forces prepared to retake Russia's Kursk region from Ukraine

Russia has amassed a large force of tens of thousands — including recently arrived North Korean troops — to carry out an assault on the Ukrainian positions in Russia's Kursk region expected in the coming days, a US official told CNN on Sunday.

Ukrainian President Volodymyr Zelensky said on Thursday that about 11,000 North Korean soldiers are in the region, where Ukraine's three-month military incursion into Russian territory has stalled.

The New York Times reported on Sunday that some 50,000 Russian and North Korean troops are set to take part in the assault.

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CNN has reached out to the Ukrainian government for comment.

A Ukrainian commander told CNN on Sunday that North Korean troops were taking part in direct combat operations in Kursk, as well as defensive operations in the neighbouring Belgorod region of Russia and in Russian-occupied Ukrainian territories.

"Mostly, the tasks are defined as the second echelon of defence. In the Kursk region, these are direct combat operations," he said, adding that among the personnel were specialist artillerymen and snipers.

"These groups will be directly involved in combat operations in the short term on the territory of Ukraine. They are highly likely to emerge in the occupied territories of Ukraine as well," the commander said.

He said the North Korean troops were a "significant resource" for Russia's war on Ukraine, as even those being deployed defensively would free up Russian troops for assault operations elsewhere and would themselves eventually be used in direct combat.

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"In military terms, they amount to three full-blooded brigades. Imagine that now the enemy withdraws 10,000 soldiers from the second line of defence, puts soldiers from North Korea there, and sends these three brigades to one of the (places where) active hostilities are underway. Are three full-blooded brigades a significant resource? Yes, it is a significant resource," Fedorenko said.

Reports that North Korea was sending troops to Russia began appearing last month, though both countries dismissed the allegations at the time.

Russia and North Korea, both pariahs in the West, have forged increasingly friendly ties since Moscow's 2022 invasion of Ukraine. North Korea has one of the world's largest militaries with 1.2 million soldiers, but most of its troops lack combat experience.

Ukraine invaded the Kursk region over the summer, shocking Russia, in the first invasion of the country since World War II.

But Ukraine's incursion hasn't stopped Russia's steady advancement in the eastern part of Ukraine, where its army chief has warned his forces are facing "one of the most powerful Russian offensives" since the start of the war.

Moscow is also unleashing near-constant waves of long-range drone strikes on Ukrainian cities and firing decoy drones without warheads to overwhelm Ukraine's air defences, according to a spokesperson for Ukraine's air force.

The Ukrainian president said from Budapest on Thursday that world leaders are not listening hard enough to his pleas to allow Kyiv to use long-range weapons as it faces a "new wave of escalation" involving "the army of another state in the war against Ukraine."

All of this comes amid questions about Ukraine's future with US President-elect Donald Trump set to take office in January.

Trump has promised to end the war in "24 hours."

Throughout his election campaign, Trump and his running mate, Ohio Senator JD Vance, cast doubts on continued US commitment to Kyiv.

They made comments suggesting the US could pressure Ukraine into an uneasy truce with Russia, causing Kyiv and its NATO allies to brace for the possibility of a dramatic reduction in US support two and a half years after Moscow invaded.

On Thursday, Russian President Vladimir Putin made his first public comments on the US election, saying he is ready for dialogue with the Republican president-elect and noting that Trump's comments on ending Russia's war in Ukraine "deserve attention at the very least."

Trump and Zelensky spoke the day after the election when the Ukrainian president called to congratulate the president-elect for what a source briefed on the call described as a positive conversation.

Trump put the call on speaker, and tech billionaire Elon Musk joined the conversation. The call was roughly seven minutes long, and no policy was discussed, according to a source with knowledge of the situation.

Meanwhile, the Biden administration on Friday lifted a de facto ban on American military contractors deploying to Ukraine to help the country's military maintain and repair US-provided weapons systems, an official with direct knowledge of the plan told CNN.

The move allows the Pentagon to provide contracts to American companies for work inside Ukraine for the first time since Russia invaded in 2022.