When North Korean troops began arriving in Russia this fall, some Western officials believed it was a sign that the Kremlin had reached out in a desperate need for more soldiers.

But U.S. intelligence agencies have now assessed that the deployment was North Korea’s idea and not Russia’s, though President Vladimir V. Putin quickly embraced it, American officials say.

North Korea’s leader, Kim Jong-un, has sent at least 10,000 troops to Russia, according to Ukrainian and Western estimates.

The North Koreans have largely embedded with Russian units mounting a counteroffensive against a contingent of Ukrainian soldiers that has been holding territory in the Kursk region of Russia since the summer.

U.S. officials do not believe Mr. Kim has received anything immediate in return. Instead, they say, he appears to be hoping that Russia will repay the favor in the future by offering support in diplomatic fights, assisting if a crisis breaks out and providing technology.

According to American and Ukrainian officials, the North Korean troops have now entered the fight in a major way, and some have been killed.