Malaysia has declared North Korea's ambassador persona non grata over the alleged murder of the North Korean leader Kim Jong-un's half-brother and ordered the diplomat to leave the country within the next 48 hours.

Kang Chol's expulsion came on Saturday, just weeks after Kim Jong-nam was allegedly poisoned at Kuala Lumpur airport on February 13.

"The expulsion of the DPRK [North Korea] ambassador is... an indication of the government's concern that Malaysia may have been used for illegal activities," Malaysia's foreign ministry said in a statement.

The decision was made after he failed to appear at Malaysia's foreign ministry at 6pm local time on Saturday despite being summoned, said Al Jazeera's Florence Looi, reporting from Kuala Lumpur.

"[Authorities] were also expecting North Korea to issue an apology because of the accusations they were making against Malaysia. But that also didn't happen, so they took this drastic measure they said."

Kim Jong-nam died after falling suddenly ill at Kuala Lumpur International Airport, where he was allegedly attacked by two women who, according to Malaysian police, smeared his face with VX, a chemical classified by the UN as a weapon of mass destruction.

He was at the airport to fly to Macau, where he had a home.

In late February, Kang Chol accused Malaysia of colluding with "hostile forces" to harm North Korea, after rival South Korea said North Korea had orchestrated the attack that killed Kim Jong-nam.

Following the incident, Malaysia summoned Chol as well as cancelled a rare visa-free travel deal with North Korea and recalled its ambassador to Pyongyang.

South Korea's spy agency believes North Korea was behind the alleged murder, but has produced no evidence.

'A conspiracy plot'

In another development on Saturday related to the case, one of the suspects said he was a victim of a conspiracy by Malaysia aimed at damaging North Korea's "honour".

Speaking to reporters outside the North Korean embassy in Beijing, Ri Jong-chol said: "I realised that this is a conspiracy plot to try to damage the status and honour of the republic."

He said he was presented with false evidence while in Malaysia.

Ri, who was deported to China on Friday after being released by Malaysian police a day earlier, denied accusations that his car was used in the case.

Insisting that he was not at the airport on the day of Kim Jong-nam's death, he said: "I had no reason to go. I was just doing my work."

Ri said he worked in the soap-manufacturing industry.

Kim Jong-nam and Kim Jong-un are sons of former leader Kim Jong-il, who died in late 2011, but they had different mothers.

Analysts in Seoul say Kim Jong-un probably had his brother killed because he could be a potential challenger to his rule in a country.

North Korea has a history of ordering killings of people it views as threats to its government.

While Kim Jong-nam was not thought to be seeking influence, his position as the eldest son of the family that has ruled North Korea since its founding could have made him appear to be a danger.