North Korea has executed five senior security officials, according to South Korea's intelligence agency.

The National Intelligence Service (NIS) said in a private briefing to politicians that the officials were killed by anti-aircraft guns for making false reports to leader Kim Jong Un.

The NIS has a mixed record when reporting on North Korean intelligence, and it is unclear what false reports the officials allegedly made.

The comments come as Malaysia investigates the poisoning of Kim's estranged half brother, Kim Jong Nam.

Investigations are ongoing, but South Korea has said it believes that Kim Jong Un ordered the assassination.