In December last year, over 11,000 North Korean troops had been deployed in Russia's Kursk region to aid Russian forces in foiling Ukrainian counterattacks in the ongoing Russia-Ukraine war.

South Korea’s assessment comes as Ukraine’s stout defence takes a growing toll for every square kilometre Russia seizes.

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 had been missing from combat, fueling speculation they were pulled back after taking heavy losses.

This is almost certainly primarily due to heavy losses sustained during attacks against Ukrainian-held positions.” Reports differ on the scale of the losses but one put them as high as 4,000 North Korean soldiers killed or wounded.

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.

South Korea's National Intelligence Service has reportedly confirmed that North Korea has withdrawn its troops from the frontline in Russia's Kursk region after entering the war late last year