North Korea confirmed for the first time on Monday that it has sent troops to fight for Russia in the war with Ukraine under the order of leader Kim Jong-un and made an important contribution to the liberation of Russian territory occupied by Ukraine.

The victorious end of the battle to liberate Russia's Kursk region showed the "highest strategic level of the firm militant friendship" between North Korea and Russia, KCNA state news agency cited the North's ruling party as saying.

Russia said last week Ukrainian forces had been expelled from the last Russian village they had been holding, although Kyiv denied the claim and said their troops were still operating in Belgorod, another Russian region bordering Ukraine.

The Central Military Commission of the North's ruling Workers' Party said leader Kim Jong-un made the decision to deploy troops under the comprehensive strategic partnership treaty he signed with Russian President Vladimir Putin last year.

"Under the order of the head of state, the sub-units of the armed forces of the Republic regarded the territory of Russia as the one of their country and proved the firm alliance between the two countries," KCNA cited the commission as saying.

WATCH | 2 captured North Korean soldiers interrogated in Kyiv, Ukraine says:

2 captured North Korean soldiers interrogated in Kyiv, Ukraine says

Ukraine has released a short video that it says are of two North Korean soldiers being questioned in Kyiv after being taken as prisoners of war in Kursk, Russia.

"They who fought for justice are all heroes and representatives of the honour of the motherland," the state news agency quoted Kim as saying.

North Korea "regards it as an honour to have an alliance with such a powerful state as the Russian Federation," KCNA said.

North Korea sent an estimated total of 14,000 troops, including 3,000 reinforcements, to replace its losses, Ukrainian officials have said. Lacking armoured vehicles and drone warfare experience, they took heavy casualties but adapted quickly.

Russia confirmed on Saturday for the first time that North Korean soldiers have been fighting alongside Russians in Kursk. Neither Russia nor North Korea had previously either confirmed or denied the deployment.