Kuala Lumpur (AFP) - Malaysia issued an arrest warrant for a North Korean airline employee Friday over the assassination of the half-brother of Pyongyang's leader, after frustrated police had to release their only other suspect from the isolated nation.

Ri Jong-Chol is among eight North Koreans suspected of involvement in the dramatic killing of Kim Jong-Nam, the half-brother of the reclusive nation's leader, who was poisoned with a banned nerve agent at Kuala Lumpur International Airport.

Malaysia's attorney general had announced there was insufficient evidence to charge 47-year-old Ri.

The North Korean was deported Friday night, a government official, who asked not to be named, confirmed to AFP.

"He will be escorted by two North Korean officials to Beijing and from Beijing to Pyongyang," deputy prime minister Ahmad Zahid Hamidi told reporters earlier. "We have also blacklisted him and he cannot enter this country again."

"The police probe showed he was not working as stated in his documents but was involved in illicit activities detrimental to our security."

Earlier, as he was led out of a police station outside the capital under tight security and handed over to immigration authorities, police chief Khalid Abu Bakar said he regretted the release.

"We believe that Ri Jong Chol played a part in Kim Chol's murder but unfortunately we lack evidence to charge him," he told AFP, using the name given in the passport carried by Kim Jong-Nam.

"We are frustrated because of a lack of evidence," he said via text message from Saudi Arabia where he is on a religious pilgrimage.

However, he denied political or diplomatic pressure had been a factor in the release, saying it was purely an investigative issue.

Ri's release came two days after two women -- one Vietnamese and one Indonesian -- were charged with murdering Kim.

Seven other North Koreans are wanted in connection with the killing.

- Arrest warrants -

On Friday police issued an arrest warrant for a North Korean airline employee, Kim Uk Il, 37, in connection with the murder.

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They also requested that Hyon Kwang Song, second secretary at the North Korean embassy, assist the probe.

Both are believed to be in Malaysia. Four others are thought to have fled to Pyongyang on the day of the murder.

Ri was arrested days after Kim suffered an agonising death when he was attacked as he waited to board a flight to Macau.

CCTV footage shows two women approaching the heavyset 45-year-old and apparently smearing his face with a cloth.

Police say he suffered a seizure and died less than 20 minutes later. Swabs of the dead man's face revealed traces of VX, a synthetic chemical so deadly that it is classed as a weapon of mass destruction.

Indonesian Siti Aisyah, 25, and Doan Thi Huong, 28, from Vietnam, face the death penalty if found guilty. Both women say they thought they were merely taking part in a prank video.

South Korea has pointed the finger of blame at North Korea, citing what they say was a standing order from leader Kim Jong-Un to kill his exiled half-brother who may have been seen as a potential rival.

North Korea, which has not acknowledged the dead man's identity, has vehemently protested the investigation, saying Malaysia is in cahoots with its enemies.

In response, Malaysia has cancelled a visa-free travel deal with North Korea -- a key conduit to the outside world -- and recalled its envoy to Pyongyang.

- 'The facts remain' -

On Thursday a senior North Korean diplomat leading a delegation to Kuala Lumpur reiterated Pyongyang’s assertion that Kim had died of a heart attack, dismissing the use of a nerve agent, and urged Malaysia to release his body.

Police chief Khalid quashed the claims.

"Our investigations supported by expert reports confirmed that Kim was murdered. North Korea can say what they like but the facts remain," he told national news agency Bernama.

Malaysia on Friday also stepped up its criticism of the use of the banned nerve agent, condemning "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," the foreign ministry said, adding that the Hague-based Organisation for the Prohibition of Chemical Weapons was helping it investigate.