Kim Jong-nam, the half-brother of North Korea's leader, died about 20 minutes after being poisoned by a nerve agent at Kuala Lumpur airport, according to an official postmortem report by Malaysian authorities.

S Subramaniam, Malaysia's health minister, said on Sunday in the capital Kuala Lumpur that an autopsy revealed that Kim Jong-un's sibling died due to a large amount of VX in his body.

VX is considered to be the most toxic nerve agent ever produced.

It is classified by the UN as a weapon of mass destruction, can paralyse the nervous system and kill by suffocation within a half-hour after exposure either through direct skin contact or inhalation.

"The amount of the VX was so high that it affected his heart and lungs. The absorption was very rapid, and that resulted in him being killed in 15 to 20 minutes" after exposure, Subramaniam said.

Postmortem complete

Subramaniam said the victim's relatives had still not travelled to Malaysia to verify Kim's identity.

He said if no next-of-kin was available, other methods would be used to confirm the identity, such as dental profiling and photo comparisons where identifications can be made via marks such as moles.

Subramaniam also said the postmortem, excluding the verification process, was complete and would be handed over to Malaysian police for further investigation.

Kim died after falling ill on February 13 at Kuala Lumpur International Airport after two women allegedly wiped his face with the nerve agent.

Separately, Hilmi Yahaya, deputy health minister, said that the VX found in Kim's body has never before been seen in Malaysia's recorded history.

READ MORE: Who produced the VX poison that killed Kim Jong-nam?

He said the nerve agent was difficult for immigration or customs officers to detect in small amounts.

VX is an extremely toxic, odourless, tasteless liquid with a brownish colour that has been used in chemical warfare and can be fatal through direct skin contact or inhalation.

It is substantially more potent than the nerve agent sarin, but works in a similar way.

The official postmortem report came as Malaysian authorities questioned a number of detained suspects, including a North Korean national suspected of producing the VX used to kill Kim.