Ukraine is fighting a war against two nuclear weapons countries: Russia, a signatory of the non-proliferation treaty, and North Korea, which is not. Since 2014, Moscow has been undermining the logic and letter of the Nuclear Non-Proliferation Treaty (NPT) with its nuclear posturing.

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engaged in combat since mid-January, South Korea's spy agency told AFP on Tuesday, after Ukraine claimed they had been withdrawn following heavy losses.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.

A Ukrainian news outlet has published a video showing the capture of a North Korean soldier, as South Korea's spy agency said Kim Jong Un has pulled troops from Russia's Kursk region. Newsweek has contacted the Russia's Foreign Ministry for comment.