Ukrainian President Volodymyr Zelensky has said his army’s continued incursion into Russia’s Kursk region is now holding back 50,000 Russian troops.

In his daily address to the nation, Zelensky said the operation reduced Moscow’s ability to strike inside Ukraine itself. The president has long called this the goal of the offensive, despite skepticism from some Western allies.

Russia had 11,000 troops in Kursk when Ukraine began its shock invasion in early August, according to the Institute for the Study of War, a U.S. nonprofit.

However, a report in the New York Times suggests that Moscow achieved its troop build-up in Kursk without the need to withdraw its soldiers from Ukraine.

The newspaper says North Korean troops are also being deployed in Kursk as part of a threatened Russian counter-offensive.

In his speech, Zelensky said he had been briefed by his commander-in-chief, General Oleksandr Syrskyy, who announced earlier on Monday that he had carried out an inspection of Ukrainian units deployed in Kursk.

“Our men are holding back… 50,000 men of the occupying army, who cannot be deployed in other Russian offensive directions on our territory due to the Kursk operation,” the Ukrainian president said.

General Syrskyy said separately that without Ukrainian forces in Kursk, “tens of thousands of enemies of the best Russian strike units” would have stormed Ukrainian positions in the Donetsk region, a key battlefield since the conflict broke out a decade ago.

Fighting continues in Donetsk, where the two sides accused each other on Monday of damaging a dam near the Ukrainian-occupied town of Kurakhove. Russian troops have been slowly advancing in the region for months towards the main city of Pokrovsk, a key supply hub for Ukrainian forces.

The New York Times, citing both American and Ukrainian unnamed officials, estimates the number of Russian and North Korean troops preparing for the reported counter-offensive in Kursk at 50,000.

“A new US assessment concludes that Russia has consolidated forces without having to withdraw soldiers from eastern Ukraine – its main priority on the battlefield – allowing Moscow to apply pressure on multiple fronts at once,” the paper said.

Both Ukraine and the US say more than 10,000 North Korean soldiers have been sent to Russia. Moscow neither confirms nor denies that troops from North Korea, a close ally since Soviet times, are in Kursk.

In North Korea itself, it was announced that its leader, Kim Jong Un, had signed a decree ratifying a mutual defense treaty with Russia, which was approved in June at a summit in Pyongyang with Russian President Vladimir Putin.

North Korea and Russia have grown increasingly close since Moscow became largely internationally isolated after invading Ukraine in February 2022. The US has repeatedly accused Pyongyang of sending vast amounts of military equipment to Russia, including ballistic missiles and launchers.

NATO Secretary General Mark Rutte recently suggested that Pyongyang was military technology and other support of Moscow to help it avoid international sanctions

Elsewhere, amid much speculation about the impact of Donald Trump’s re-election victory last week, the Kremlin has denied media reports that he held a phone call with President Vladimir Putin.

The call, first reported on Sunday by the Washington Post, is said to have taken place on Thursday. Trump reportedly warned the Russian president about an escalation of the war in Ukraine and mentioned America’s extensive military presence in Europe.

Trump’s team told the BBC it would not comment on the president-elect’s “private conversations.”