Since then, Russian forces – bolstered by thousands of North Korean troops sent by Putin-ally Kim Jong-un – have sought to claw back most of that land. The North Korean troops began arriving in Kursk from late October as part of a mutual defence pact agreed between Putin and Kim.

After clinging for more than seven months to a gradually shrinking area, Ukraine has seen its position worsen sharply in the past week.

Russia said on Thursday there was no doubt that its troops would soon complete the task of clearing out Ukrainian forces from Russia's Kursk region where they have held a pocket of territory for more than seven months.