Pyongyang is believed to have sent some 11,000 soldiers to help Putin’s army recapture a swathe of the Kursk region of Russia which Ukrainian forces seized in a surprise attack last summer. The Russian military has been gradually gaining ground in the attempt to force Ukrainian units out of Kursk.

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.

"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.

North Korean missiles used by Russia in attacks on Ukraine since December have become more accurate, Reuters reported on Feb. 6, citing sources familiar with the matter. Analysts believe North Korea is using the battlefield as a testing ground for its missile technology,

Experts say Pyongyang’s advancing missile technology raises global security risks and threatens regional stability.