Police in Malaysia have named a senior official in North Korea's embassy and a staffer at its state airline, who are wanted for questioning over the murder last week of Kim Jong-nam, the estranged half-brother of North Korea's leader.

Kim Jong-nam was killed at Kuala Lumpur International Airport on 13 February, while preparing to board a flight to Macau, where he lived in exile with his family under the protection of Beijing.

South Korean and US officials believe the killing of the elder half-brother of Kim Jong-un was an assassination carried out by agents of North Korea.

Kim Jong-nam had spoken out publicly against his family's dynastic control of the isolated, nuclear-armed state.

Malaysia's police chief Khalid Abu Bakar said the diplomat wanted for questioning was 44-year-old Hyon Kwang Song, a second secretary at the embassy.

Police also want to interview Kim Uk Il, 37, an employee of the North Korean state-owned airline Air Koryo.

Mr Khalid said both were in Malaysia but could not confirm they were in the embassy.

"They've been called in for assistance. We hope the embassy will co-operate with us and allow us to interview them quickly or else we will compel them to come to us," he told reporters at a news conference.

Police have stepped up security at the morgue where Kim Jong-nam's body is being held after an attempted break-in earlier this week, police said.

Malaysia has denied North Korea's request for the body to be handed over to its embassy directly and has urged the victim's next of kin to come forward to help with the investigation.

Malaysia has so far identified a total of eight North Koreans suspected of being linked to killing.

One man is in custody while another is still at large and police believe four others were back in the North Korean capital of Pyongyang, having fled Malaysia on the day of the attack.

Police have not stated the role of the man in custody in the killing.

He lived in Malaysia for three years without working at the company registered on his employment permit or receiving a salary.

The first suspects to be arrested last week were two women - one Vietnamese, one Indonesian - who are suspected of carrying out the fatal assault on Kim Jon-nam using a fast-acting poison.

Police said both women wiped a liquid, containing an as yet unidentified toxic substance, on Kim Jong-nam's face.

"Yes, the two female suspects knew that the substance they had was toxic. We don't know what kind of chemical was used," the police spokesman said, dismissing speculation that the women had thought they were part of a prank.

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

The women had rehearsed the attack at two shopping malls in central Kuala Lumpur before assaulting Kim Jong-nam, he said.

Diplomatic tensions have escalated between North Korea and Malaysia since the killing, with the countries trading barbs over Malaysia's handling of the investigation.

North Korea Malaysia is one of the few countries in the world that maintains ties with the nuclear-armed nation.

Journalists at the entrance to the North Korean Embassy in Kuala Lumpur

Earlier this week Malaysia recalled its ambassador from Pyongyang, and Prime Minister Najib Razak rebuked the North Korea ambassador in Kuala Lumpur for making "diplomatically rude" comments.

The police said no family member of Kim Jong-nam has come forward to claim the body or provide DNA samples yet, dismissing rumours that a son had arrived in Kuala Lumpur earlier this week.

Malaysia has said it will only release the body to the next-of-kin once the cause of death and identity have been confirmed.