Malaysia has condemned the use of toxic nerve agent VX that killed the estranged half-brother of North Korea's leader at an airport packed with travellers, as authorities moved to deport a North Korean suspect.

Kim Jong-nam was murdered on February 13 at Kuala Lumpur International Airport, where he was assaulted by two women who allegedly smeared his face with VX, a chemical classified by the United Nations as a weapon of mass destruction.

Malaysia's foreign ministry "strongly condemns the use of such a chemical weapon by anyone, anywhere and under any circumstances. Its use at a public place could have endangered the general public", it said in a statement on Friday.

Who produced the VX poison that killed Kim Jong-nam?

North Korea has denied accusations that it was involved in the killing. It described as "absurdity" the belief that VX was used and suggested the victim died from heart failure.

Malaysia's foreign ministry said it was in close contact with the Organisation for the Prohibition of Chemical Weapons (OPCW), an inter-governmental organisation based in the Netherlands, regarding the incident.

"Malaysia does not produce, stockpile, import, export or use any Schedule 1 toxic chemicals, including VX, and has made annual declarations to that effect to the OPCW," the statement said.

North Korean diplomat Ri Tong-il - who is leading a delegation to the country - said on Thursday that Malaysia should provide samples of the VX that police say they found on the body to the OPCW.

"If it is true that it was used," he told reporters, "then the samples should be sent to the office".

Ri, a former North Korean deputy ambassador to the UN, said it made no sense to say the two women used such a deadly toxin without also killing or sickening themselves - and people around them.

He added that Kim had a history of heart problems and had been treated in hospital in the past. He said that he understood that Malaysian officials found medication for diabetes, heart problems, and high blood pressure in Kim's belongings and concluded that he wasn't fit to travel.

"This is a strong indication that the cause of death is a heart attack," Ri said.

Malaysia to cancel visa-free entry for North Koreans

Relations between Malaysia and North Korea, who have maintained friendly ties for decades, have soured since the killing of Kim Jong-nam, the estranged brother leader Kim Jong-un, who had lived for years in exile in Macau.

South Korean intelligence and US 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.

They face the death penalty if convicted. They have told diplomats from their home countries that they thought they were participating in a prank for reality television.

Al Jazeera's Florence Looi, reporting from Kuala Lumpur, said questions remain about who else may have been involved with the women.

"There are doubts they could have acted on their own because how would have they been able to obtain the highly toxic substance that was found on Kim Jong-nam's body and apparently killed him," said Looi.

Another North Korean suspect, who was arrested on February 18 over the killing, was released from a detention centre on Friday and driven away in a police convoy.

Kim Jong-nam 'died about 20 minutes after VX poisoning'

Ri Jong-chol was taken to the immigration office wearing body armour to prepare for his deportation to North Korea.

Malaysia's attorney general said on Thursday that he would be released because of insufficient evidence.

Police have identified seven other North Koreans wanted in connection with the killing, including a senior embassy official in Kuala Lumpur. Four have left the country and are believed to be in Pyongyang.