North Korea is gaining crucial military experience and equipment by sending troops to Russia, a U.S. official warned the United Nations, making the regime a growing threat to neighboring countries.

The wounded fighters were taken to Kyiv for questioning, authorities said, where they could reveal details of Pyongyang’s cooperation with Moscow.

President Volodymyr Zelensky said the soldiers were captured in the western Kursk region, where Ukraine has been fighting to hold on to territory it seized last summer.