Hundreds of North Korean troops were likely transported by sea to Russia to fight in its war against Ukraine, satellite images have revealed, according to a new analysis from a US-based think tank shared exclusively with CNN.

Ukrainian troops holding positions in Kursk say the North Koreans have reappeared on the battlefield and become even more formidable foes.

North Korea has deployed thousands of troops to support Russian forces fighting in Ukraine, according to Ukrainian, U.S. and South Korean assessments, Pyongyang's first major involvement in a war since the 1950s.