Though North Korean ballistic missiles account for only a small portion of Russia's missile strikes they carry a large warhead of up to one tonne and have a range of up to 800 km, the military source said. The Iskander-M, an equivalent Russian missile, carries a smaller payload and has a shorter range of 500 km.

North Korean soldiers previously fighting alongside Russia's army on the Kursk front line appear not to have been engaged in combat since mid-January, South Korea's spy agency told AFP on Tuesday, after Ukraine claimed they had been withdrawn following heavy losses.

Ukrainian special operations forces have given an insight into the brutal, near-suicidal tactics of the North Koreans they have faced in intense fighting in the Russian border region of Kursk.

Captured North Korean soldiers have lifted the curtain ever so slightly on the secretive Kim regime’s decision to join Russia’s war against Ukraine.

"The worst problem we are facing is the one coming from North Korea," the head of Kyiv's military intelligence agency said in the fall.

It also shed some light on the mindset and training of the conscripted North Korean soldiers sent to fight Russia’s war a continent away from their home. Highly disciplined, ready to die but also very young and with little battlefield experience they elicited curiosity and even some pity from the Ukrainian soldiers who captured them during two separate missions on Jan.