Malaysia has labelled North Korea "delusional" over claims that include the man assassinated at Kuala Lumpur airport last week was not the estranged half-brother of North Korea's leader Kim Jong-un.

Foreign minister Anifah Aman said Malaysia is "deeply insulted" by North Korea's questioning of the investigation into the poisoning of 46 year-old Kim Jong-nam by two women in what South Korea says was a long planned operation by North Korea's spy agency.

Mr Anifah hit back in a statement saying "these allegations are culled from delusions, lies and half-truths."

"In all civilised nations, it is the norm for cases such as these to be comprehensively investigated," he said.