National Intelligence Service Director Cho Tae-yong walks to attend a closed-door session with lawmakers at the National Assembly in Seoul, Dec. 19. Yonhap

South Korea's spy agency on Thursday said at least 100 North Korean troops dispatched to Russia for combat in Ukraine were killed and 1,000 injured, according to a lawmaker.

In a closed-door briefing to the parliamentary intelligence committee, the National Intelligence Service (NIS) also said the Russian military has complained that the North Korean troops lack drone response capabilities and are mainly mobilized as front-line storm troopers.

Some of the estimated 11,000 North Korean soldiers deployed in the Kursk region began to be mobilized into actual combat in January and February, according to the NIS.

The agency also said it has detected signs North Korean leader Kim Jong-un is making preparations to train a special operation force to additionally dispatch to Ukraine. (Yonhap)