According to Malaysian authorities, a deadly VX nerve agent was smeared on Mr Kim's face
North Korea has said a heart attack – rather than a nerve agent - probably killed Kim Jong-Nam in Malaysia last month.
Pyongyang has also yet to accept that the man who died at Kuala Lumpur international airport is Mr Kim, the half-brother of North Korean leader Kim Jong-Un.
According to police in Malaysia, two women smeared a deadly VX nerve agent on Mr Kim's face on 13 February then fled in a cab.
Two women, an Indonesian and a Vietnamese, have been charged and could face the death penalty if found guilty.
They claim they were tricked into killing the 45-year-old after being told it was a prank for a TV show.
A North Korea envoy sent to Kuala Lumpur has disputed Malaysia's verdict on Mr Kim's cause of death.
Speaking to reporters outside the embassy, Ri Tong Il questioned the alleged use of VX, saying samples should be sent to the Organisation for the Prohibition of Chemical Weapons (OPCW).
"If it is true that it was used, then the samples should be sent to the office of OPCW," said Mr Ri, a former North Korean deputy ambassador to the UN.
"In case it is proved by the two separate international laboratories, with the same conclusion, then they should come to identify who is the one that made it. Who is the one that brought it into Malaysia."
He said the victim had a history of heart disease, and appeared to have been taking medicines for high blood pressure and diabetes.
"Therefore this is a strong indication the cause of the death is the heart attack," he said.
Malaysia also arrested a North Korean man, Ri Jong Chol, but now says it will deport him on Friday because there is not enough evidence to charge him.
South Korean intelligence officials say the murder was an assassination organised by North Korea because the victim was perceived at one point to be a threat to Kim Jong-Un's grip on power.
Mr Kim had advocated reform in the nation, but had kept a largely low profile for years. He lived in Macau under Chinese protection.
Pyongyang has said it is the target of a smear campaign and that it cannot trust the Malaysian investigation.
The killing has soured relations between North Korea and Malaysia, which was until recently one of the few nations to maintain friendly ties with the reclusive regime.
Kuala Lumpur has also said it will cancel visa-free entry for all North Koreans.