The Ukrainian special forces which are fighting in the region of western Russia told the BBC that they had not seen any North Korean troop for three weeks.
A spokesperson said it was likely that they had withdrawn after undergoing heavy losses.
Last week, Western officials told the BBC that, out of some 11,000 soldiers sent from North Korea to fight for Russia, 1,000 had been killed in just three months.
North Korea and Russia have not commented.
On Friday, the spokesperson for the Ukrainian special forces told the BBC that he was referring only to the areas of the Kursk region where his forces were fighting.
The spokesman did not say how long this front line was.
And although this is not the full table, he suggests important North Korean victims.
In addition, the New York Times also reported that the North Koreans had been removed from the front lines.
The newspaper cited American officials saying that the withdrawal may not be permanent, and soldiers could return after receiving additional training or after the Russians have found new ways to deploy them to avoid such victims.
The reports attributed to South Korean intelligence say that North Koreans are not prepared for the realities of modern war and are particularly vulnerable to be targeted by Ukrainian drones.
Russian President Vladimir Putin and the North Korea chief Kim Jong Un has deepened bilateral ties, signing a security and defense treaty.
The help of Pyongyang in Moscow also also extends to large amounts of ammunition and weapons.
Last August, Ukrainian elite troops launched a lightning offensive in Kursk, entering more than 1,000 km2 (386 miles m²) of Russian territory.
Since then, the Russian forces have managed to resume an important part of this region.
Kyiv’s surprise foray was aimed at modifying the dynamics of war.
It was initially hoped that the operation would relieve the pressure on other parts of the first line more than 1,000 km long (620 miles), in particular in eastern Ukraine.
Moscow continues its relentless – although slow – east, leading a number of colonies in the Donetsk region in recent weeks.
Now Kyiv seeks to keep the ground he occupies in Kursk as a lever for any ceasefire or peace negotiations with Moscow.
Russia launched a large -scale invasion of Ukraine in February 2022.
