Ukrainian President Volodymyr Zelenskyy says more than 3,000 North Korean soldiers have been killed or wounded in the fighting in the western Russian region of Kursk.

Zelenskyy said in a social media post on Monday that the figure was reported by Ukraine's military Commander-in-Chief Oleksandr Syrskyi.

Ukraine is waging a cross-border offensive in the Kursk region. About 11,000 North Korean soldiers are said to be deployed alongside Russian troops in the area.

Zelenskyy called for international action, writing that "unfortunately, the world is doing almost nothing to counter the criminal collaboration between Russia and North Korea."

The number of North Korean casualties mentioned by Zelenskyy far exceeds the figure given by South Korea's intelligence agency last week.

The agency estimated that at least 100 North Korean soldiers have been killed fighting for Russia in Kursk. It said around 1,000 more have been wounded.