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.

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.

North Korean troops, largely special ops forces, have suffered high casualties in bloody assaults not unlike other units, including prison units.

Kyiv is open to negotiating with South Korea over the possible transfer of captured North Korean soldiers, Ukrainian Ambassador to Seoul Dmytro Ponomarenko said in an interview with The Korea Times published on Feb.

A North Korean soldier captured fighting for Russia in Ukraine last month reportedly made just two requests to his captors - one for water and another for a cigarette

One Ukrainian special forces soldier shares details of how his team captured the North Korean, giving an insight into the North Korean mindset.