Zelenskyy said last month that 11,000 North Korean troops were in Russia’s western Kursk region and had already sustained “losses”.
Washington and Seoul have accused Pyongyang of sending more than 10,000 soldiers to help Moscow, after Russia and North Korea signed a landmark defence pact this summer.
North Korea and Russia have strengthened their military ties since Moscow’s invasion of Ukraine in February 2022.
Taken by surprise by the Kursk incursion, Russia has since steadily clawed back territory, halting Ukraine’s advance and rushing reinforcements to the region.
A Ukrainian army source told AFP last month Kyiv still controlled 800 square kilometres of the Kursk region, down from previous claims it controlled almost 1,400 square kilometres.
