Russian President Vladimir Putin, right, and North Korea's leader Kim Jong Un agreed to a mutual defence pact last year.North Korea has suffered more than 5,000 casualties in the Ukraine war, according to UK intelligence.Around one-third of them have been killed in action while fighting for Russia, the Ministry of Defence said in its latest update on the conflict.North Korean leader Kim Jong Un sent around 11,000 fighters to help Russia last November.They have been fighting in Kursk, the Russian territory invaded by Ukraine in a surprise move last year.The MoD said: “As of March 2025, Democratic People’s Republic of Korea (DPRK) forces had highly likely sustained over 5,000 casualties in offensive combat operations against Ukrainian forces in the Russian oblast of Kursk, with approximately a third of the casualties killed in action.”Although the Russian and North Korean troops have gained territory in recent weeks, the MoD said Ukraine still has “at least a foothold” in the region.