The move gives Kim Jong-un, the leader of North Korea, leverage to ask President Vladimir V. Putin of Russia for a lot in return.

The U.S. government said it had evidence that at least 3,000 North Korean soldiers were being trained in Russia.

The first group of North Korean troops have been sent to the Russian region of Kursk where some have tried to desert, according to reports. Ukraine launched an incursion into the Russian region on August 6 and Putin is said to be planning to use the North Korean soldiers in his fight to recapture territory.