At least 600 North Korean soldiers died during that offensive and thousands more sustained injuries, according to South Korean estimates.
Moscow and Pyongyang spent months denying and ignoring Western reports of the deployment.
Only in April, when Russia declared it had expelled Kyiv’s forces, did Putin publicly acknowledge the role of the “heroic” North Koreans who fought alongside his army.
North Korea also acknowledged the deployment and, for the first time since its founding in 1948, acknowledged it had lost soldiers on foreign soil.
Earlier this month, North Korean state media reported that the country had started construction of a memorial for soldiers killed in the fighting.
The United States says there is evidence Russia is stepping up its support for North Korea, including providing help on advanced space and satellite technology.
Ukraine says it has found fragments of North Korean weapons including missiles on the battlefield.
