South Korea's spy agency said that a North Korean soldier who was captured alive in Ukraine has died from his injuries, according to the Yonhap news agency.

"It has been confirmed through an allied intelligence agency that the North Korean soldier captured alive on December 26th has just passed away due to worsening wounds," the South's spy agency said in a statement on Friday.

Earlier today, the agency confirmed that a North Korean soldier had been captured by Ukrainian forces.

This marks the first official confirmation of a North Korean combatant’s capture in the conflict.

'Breakthrough document'

South Korea's Joint Chiefs of Staff (JCS) said on Monday that more than 1,000 North Korean soldiers had been casualties and that Pyongyang is preparing for the "rotation or additional deployment of soldiers."

North Korea is also supplying Russia with advanced weaponry, including 240mm rocket launchers and 170mm self-propelled artillery.

Seoul’s military believes that North Korea is leveraging the war to modernise its conventional military capabilities through battlefield experience.

Meanwhile, North Korean state media highlighted strengthening ties between Pyongyang and Moscow, with Russian President Vladimir Putin lauding their defence pact as a "breakthrough document" and noting improved bilateral relations following talks with North Korean leader Kim Jong Un in June.