The Ukrainian Special Forces, fighting in the West Russian Corsc region, have told the BBC that they have not seen any North Korean forces there during the past three weeks.
A spokesman said that they would have withdrawn after suffering heavy losses.
Last week, Western officials told the BBC that among about 11,000 soldiers sent from North Korea to fight for Russia, 1000 were killed in just three months.
North Korea and Russia did not comment.
On Friday, the Ukrainian Special Forces spokesman told the BBC that he was only referring to areas in the Kursk area where his forces were fighting.
The spokesman did not say about the time that this front line spent.
Although this is not the full picture, it indicates great losses in North Korea.
Separately, the New York Times also reported that the North Koreans have been withdrawn from the front lines.
The newspaper quoted US officials as saying that the withdrawal may not be always, and soldiers can return after receiving additional training or after the Russians reach new ways to spread them to avoid such heavy victims.
Reports attributed to the South Korean intelligence say that the North Koreans are not ready to the facts of modern war, and they are particularly exposed to targeting of Ukrainian drones.
Russian President Vladimir Putin and North Korean leader Kim Jong Un have depth the bilateral relations, as they signed a security and defense treaty.
Pyongyang's assistance to Moscow is now to large amounts of ammunition and weapons.
Last August, the Ukrainian elite forces launched an attack on lightning in Corsak, and seized more than 1,000 square kilometers (386 square miles) of Russian territory.
Since then, Russian forces have been able to restore a large part of that area.
Kyiv's sudden penetration aims to change the dynamics of war.
It was initially hoped that the process would reduce the pressure on other parts of the front line, which is more than 1000 km (620 miles), especially in eastern Ukraine.
Moscow continues to progress that is uncomfortable – albeit slow – in the east, as it seized a number of settlements in the Donetsk region in recent weeks.
Kyiv is now looking to stick to the land it occupies in Kursk as a financial lever for any possible shooting negotiations or peace negotiations with Moscow.
Russia launched a large -scale invasion of Ukraine in February 2022.
