The Malaysian ambassador to North Korea believes the investigations into the death of Kim Jong-nam would be done in an impartial and professional manner.

Mohamad Nizan Mohamad, who was met by the Associated Press (AP) in Beijing, while in transit enroute to Malaysia, assured the investigations would be "objective and fair to everybody".

"I think the investigation is still ongoing, so just wait and see. And we can assure you of the impartiality of the investigation itself, because there is no reason for us to side with anybody," Nizan was quoted saying. 

The Malaysian ambassador to Pyongyang was recently called back to Kuala Lumpur for "consultations", just hours before North Korea's ambassador to Malaysia Kang Chol issued a scathing remark against Malaysia's probe into the death of Jong-nam, the older half-brother of North Korean ruler Kim Jong-un.

Kang had said that North Korea does not trust the Malaysian probe into the death, and claimed it was politically motivated, and demanded a joint probe. 

Malaysia's Foreign Minister Anifah Aman had responded to Kang's allegations, saying his comments were "culled from delusions, lies and half-truths".

Meanwhile, South Korea's Yonhap news agency reported South Korea's unification ministry rejecting the "preposterous and sophistic" claim by the North claiming that Malaysia had colluded with Seoul in investigating Jong-nam's death.

"The envoy's comment on South Korea is a preposterous claim that is not even worth countering," a ministry official was quoted saying.

This was in response to Kang, when denouncing Malaysia's finding, saying that the local authorities were "colluding and playing into the gallery of external forces".

The Malaysian police have so far arrested four suspects in connection with the murder, including a Vietnamese woman and an Indonesian woman. The two other suspects are a local man and a North Korean man. 

Four more North Korean men are also being sought in relation to the killing. 

Jong-nam was murdered at the Kuala Lumpur International Airport 2 on Feb 13, shortly before he was due to leave for Macau. 

The two female suspects were believed to have administered poison to Jong-nam, who lived in exile.