The comments by the National Intelligence Service in a private briefing to lawmakers on Monday come as Malaysia investigates the poisoning death there of Kim's estranged elder half brother, Kim Jong Nam.
That investigation is still going on, but South Korea says it believes Kim Jong Un ordered the assassination.
South Korean lawmaker Lee Cheol Woo said the intelligence agency told lawmakers that five North Korean officials in the department of recently purged state security chief Kim Won Hong were executed by anti-aircraft guns for the false reports. It's not clear what false reports they allegedly made.
The NIS has a spotty record when reporting North Korea intelligence.