The United States reportedly believes that some North Korean soldiers are in Russia’s Kursk region, where Russian troops are struggling to push back a Ukrainian incursion. 

Reuters issued the report Tuesday, citing two U.S. officials who spoke on condition of anonymity. 

But according to the report, the officials did not say what they believed the North Korean forces were doing in Kursk, and one of the officials said it was unclear how they would be aiding Russia.

Earlier on Tuesday, South Korea’s National Intelligence Service said some North Korean troops, including high-ranking military officers, may have moved to the front lines. 

On Monday the U.S. departments of State and Defense said North Korea has sent about ten-thousand troops to Russia for training, adding that some have moved closer to Ukraine.