South Korea’s spy agency said Wednesday that North Korea appears to have sent additional troops to Russia, after its soldiers deployed on the Russian-Ukraine fronts suffered heavy casualties.

Axar.az reports that citing AP, the National Intelligence Service said in a brief statement it was trying to determine exactly how many more troops North Korea has deployed to Russia.

The NIS also assessed that North Korean troops were redeployed at fronts in Russia’s Kursk region in the first week of February, following a reported temporary withdrawal from the area.

Earlier Wednesday, South Korea’s JoongAng Ilbo newspaper, citing unidentified sources, reported that an additional 1,000-3,000 North Korean soldiers were deployed to Kursk between January and February.

In January, the NIS said about 300 North Korean soldiers had died and another 2,700 had been injured. Zelensky earlier put the number of killed or wounded North Koreans at 4,000, though U.S. estimates were lower at around 1,200.