Bangkok: Malaysian police want to question a diplomat at the North Korean embassy in Kuala Lumpur over the assassination of Kim Jong-nam, the estranged half-brother of North Korean dictator Kim Jong-un.

Police chief Khalid Abu Bakar identified the diplomat as a second secretary, 44-year-old Hyon Kwang-song, who holds diplomatic immunity. Mr Khalid said police also want to question an official of North Korea's airline Air Koryo, named as Kim Uk-il, 37. He gave no further details.

He said the men, who were still in Malaysia, "are not in custody, they've being called in for assistance". Asked if they were suspects, he said "we would call them in first". He said if the men did not comply with requests to be interviewed, warrants would be issued for their arrest.

Five other North Koreans have been identified as suspects in Mr Kim's suspected poisoning at Kuala Lumpur International Airport's  low-cost terminal on February 13. The case has sparked international intrigue, rumours and a diplomatic spat.

On Wednesday, Reuters also reported an attempted break-in at the morgue where the body of Mr Kim is being held under heavily armed Malaysian police guard.

The body has been at the centre of a diplomatic tug-of-war between the two countries, with North Korea demanding it be handed over before an autopsy was carried out.

The dramatic developments came as Malaysian police said two women seen in CCTV footage, one Indonesian and the other Vietnamese, knew they were taking part in a poison attack.

Mr Kim, 46, who was about to fly to Macau, became unwell after two women appeared to wipe a cloth on his face. He died on the way to hospital.

"Yes, both women suspects knew that the substance they had was toxic. We don't know what type of chemical was used," Mr Khalid said.

"They used their bare hands," he said, adding they were instructed to wash their hands afterwards.

Mr Khalid said the women had practised the attack multiple times.

"We strongly believe it is a planned thing and that they have been trained to do that. This is not just like shooting a movie," he told reporters.

One of the women claimed they had been duped into believing they were taking part in a television prank show, Indonesian police said last week, citing information from Malaysia. 

Mr Khalid said that four North Korean men who flew out of Kuala Lumpur immediately after the attack had travelled to the North Korean capital Pyongyang.

Also in custody in Malaysia is a North Korean chemist who had been living in Kuala Lumpur with his wife and two children since 2013.

Malaysian police are awaiting the results of forensic tests to establish what substances were used in the attack.

South Korea has claimed Kim Jong-un issued a standing order five years ago to have his estranged sibling assassinated.

Kim Jong-nam had questioned his family's dynastic control of the country and called for economic reforms.

The involvement of the diplomat and airline employee, if confirmed, would point to a long-planned and elaborate assassination plot by North Korea's spy agency.

Malaysia has dismissed North Korean claims regarding the case, including that the man who died was not Kim Jong-nam. Malaysian Foreign Minister Anifah Aman said statements made  by North Korea's ambassador in Kuala Lumpur were "culled from delusions, lies and half-truths".

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