South Korea's intelligence agency says at least 100 North Korean soldiers have been killed fighting for Russia's invasion of Ukraine, with around 1,000 more injured.

The National Intelligence Service mentioned the figure when it briefed the parliamentary Intelligence Committee about its latest findings on Thursday.

A lawmaker who attended the closed-door meeting told reporters that out of the estimated 11,000 North Korean soldiers deployed in the western Russian region of Kursk, some of them joined combat earlier this month.

The lawmaker said the agency believes the level of North Korean casualties can be attributed to the fact they are being "consumed" as frontline storm troopers in "unfamiliar battlefields," and lack sufficient training in drone warfare.

The lawmaker said the agency also believes that even before the North Korean troops were sent to the frontline, some of their senior officers had died in training accidents or been killed in Ukrainian attacks.