South Korea's public broadcaster KBS says radio communications intercepted by the Ukrainian military suggest North Korean troops are taking heavy casualties during battles in the western Russian region of Kursk.

KBS on Tuesday revealed the content of radio communications from what is believed to be a North Korean soldier fighting for Russia in Kursk, where Ukrainian forces have been staging a cross-border offensive.

The conversations were reportedly intercepted by the Ukrainian military on December 20 of last year.

On the radio, a voice says it will likely take more time to recover the bodies of his comrades.

The voice says he plans to gather other soldiers early in the morning for the retrieval and seeks advice for the plan.

KBS says a number of North Korean troops were killed in fighting, and that the North's soldiers face a bleak situation, having to recover the dead bodies while hiding themselves during dark hours.

The broadcaster cites an analysis by an expert that the situation suggests poor Russian tactical support for the North Korean troops.

Ukrainian President Volodymyr Zelenskyy said in an interview released on Sunday that 3,800 North Korean soldiers have been killed or wounded so far in Kursk.