The leader of Russia's Communist Party has hailed North Korean troops deployed in Moscow's war against Ukraine in a letter sent to the North's leader Kim Jong-un, according to the North's state media Sunday.

Russian President Vladimir Putin praised North Korean troops for their “bravery, heroism and self-sacrificing spirit” on his front lines.

More than 50,000 North Koreans will be sent to work in Russia, as Moscow's war in Ukraine drains labour pools.