Malaysia will deport a North Korean held in connection with the death of Kim Jong Nam, and cancel visa-free entry for all North Koreans, as diplomatic ties between the two countries frayed further following the murder at Kuala Lumpur's airport.

The relationship between Malaysia and North Korea has soured since the estranged half brother of North Korean leader Kim Jung Un was murdered two weeks ago at Kuala Lumpur International Airport with a super toxic nerve agent VX.

South Korean intelligence and U.S. officials say the murder was an assassination organised by North Korean agents, though the only suspects charged in the case so far are an Indonesian woman and a Vietnamese woman.

Police are also holding one North Korean man and want to question seven others, including a senior official in the North Korean embassy in Kuala Lumpur.

But, the detained North Korean, Ri Jong Chol, will be deported on Friday as there is insufficient evidence to charge him, Malaysian Attorney General Mohamed Apandi Ali told Reuters in a text message on Thursday.

Ri was arrested in Kuala Lumpur on Feb. 17 with a work permit that had been valid till Feb. 6, 2017.

It is unclear what Ri's suspected role was in the murder.

Security camera footage showed two women assaulting Kim Jong Nam at the airport as he was waiting to board a flight to Macau, where he had been living with his family under Chinese protection.

Malaysian police say they smeared his face with VX nerve agent, a chemical classified by the United Nations as a weapon of mass destruction, and that Kim died within 20 minutes of being attacked.

North Korea, which has not accepted that the dead man is Kim Jong Nam, said on Thursday that there were strong indications a heart attack killed the North Korean national.

Speaking to reporters outside the embassy in Kuala Lumpur, former North Korean deputy ambassador to the United Nations 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," Ri said.

"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 added.

Ri is heading a high level diplomatic delegation that met with Malaysian cabinet ministers after arriving in Kuala Lumpur earlier this week.

North Korea had earlier tried to convince Malaysia not to perform an autopsy on Kim Jong Nam's body, and to release three suspects detained in connection with the killing.

The women, who could face the death penalty, have told diplomats from their countries that they had believed they were carrying out a prank for a reality television show.

Police say four of the other North Korean suspects have fled Malaysia. Three other suspects - a diplomat, an Air Koryo official and another North Korean - are yet to come forward.

NEAR BREAKING POINT

The two countries have maintained friendly ties for decades, but the relationship has come close to breaking point.

Malaysia has insisted that laws of the country will be followed and has refused to release the body to the North Korean embassy in Kuala Lumpur, while waiting for next of kin to come forward.

Deputy Prime Minister Ahmad Zahid Hamidi said Malaysia will cancel visa-free entry for North Koreans from March 6, in a decision taken for national security reasons.

Malaysia is one of the few countries that North Koreans could visit without a visa, and Malaysians are among the few nationalities granted visa-free entry to the secretive, nuclear-armed state.

Following a Reuters report this week that the North Korean intelligence agency has been running an arms operations from Kuala Lumpur for years, Malaysian authorities have said two North Korea-linked companies are in the process of being struck off the company registry.

North Korea and Malaysia have maintained cosy ties since the 1970s when former prime minister Mahathir Mohamad embraced the isolated state, in part to rebuff the United States.

Malaysian palm oil and rubber is exported to the communist state. Cars made by Malaysian national carmaker Proton have been sold to North Korea and used as taxis.