North Korea began sending an estimated 11,000 troops to the Russian Kursk region late last year, soon after North Korean leader Kim Jong-un and Russian President Vladimir Putin agreed on a mutual defense pact designed to strengthen their alliance against what they called a US-led “Western hegemony.”

In its first direct criticism of the Trump administration, North Korea lashed out at U.S. Secretary of State Marco Rubio for calling it a “rogue” state and warned Monday that such “coarse and nonsensical remarks” will never contribute to U.

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engaged in combat since mid-January, South Korea's spy agency told AFP on Tuesday, after Ukraine claimed they had been withdrawn following heavy losses.

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.

Thousands of North Korean troops helped Russia regain some of its territory in the Kursk region following Ukraine's counterattack, but the Russian army is now using them less on the front line and have pulled some back.

South Korea's National Intelligence Service has reportedly confirmed that North Korea has withdrawn its troops from the frontline in Russia's Kursk region after entering the war late last year

South Korea's spy agency says that North Korean forces have suffered more than 3,000 casualties while fighting alongside Russian troops.