A legal adviser to the International Criminal Court (ICC) has said that North Korea leader Kim Jong-un can be referred to the world judicial body if found to have orchestrated the killing of his estranged half brother, media report said on Thursday.

North Korea was widely believed to be behind the killing of Kim Jong-nam in Malaysia in February using deadly VX nerve agent, media reported.

"That could be something that may allow the UN Security Council or even the ICC to hold him up, if, again if, you can show that they were behind it because of the nature of, type of substance used in that," the lawyer was quoted by media as saying.

The ICC is an intergovernmental organisation and international tribunal that sits in The Hague in the Netherlands. 

"With the ICC, it always ... goes up the ladder, you find the person who was ultimately responsible. You don't actually go and charge the people at the bottom," the lawyer said. 

"So there is a precedent for ... ultimately you go for the leader who ordered even if you were not involved in actual planning. If you ordered, sanctioned the killing, that makes you liable," the legal advisor added.

In 2014, the UN General Assembly voted to refer North Korea to the ICC for crimes against humanity, after a Commission of Inquiry report documented ongoing atrocities there.

The atrocities included incarcerating over 120,000 people in political prisons, as well as systematic abuses that included torture, enslavement, rape and murder, according to the media report.