Kuala Lumpur, Malaysia (CNN) Malaysia declared the North Korean ambassador "persona non grata" and plans to expel him from the country in 48 hours, its Ministry of Foreign Affairs said Saturday.

The move comes as an investigation is underway into last month's death of Kim Jong Nam, the estranged half brother of North Korean leader Kim Jong Un.

Malaysian police say Kim Jong Nam was killed February 13 when he was smeared with a deadly VX nerve agent while waiting at Kuala Lumpur International Airport.

North Korea has vehemently denied any connection to the killing.

'Hefty price'

Diplomatic tensions between the two countries escalated last month after comments by Kang Chol, the North Korean ambassador.

He said North Korea would reject the results of a "forced" autopsy on one of its citizens, and he demanded the immediate release of the body.

Kang accused Malaysian officials of conspiring with "hostile forces" during the investigation, eliciting a harsh rebuke from his host country.

The Malaysian Ministry of Foreign Affairs said it had demanded an apology over the diplomat's accusations but had not received one.

Malaysian Deputy Prime Minister Ahmad Zahid Hamidi said earlier there would be a "hefty price" if the series of verbal attacks continued.

Women charged in death

Both women maintain they thought they were participating in a TV prank show, according to authorities from their home countries.

Aisyah thought the substance she rubbed on Kim's face was " a kind of oil, baby oil, something like that," said Andreano Erwin, Indonesia's deputy ambassador to Malaysia.

Malaysian authorities said the substance was VX nerve agent, a deadly chemical weapon banned under international law.

After the women wiped Kim's face with the liquid, he started feeling dizzy and died shortly afterward on his way to the hospital, Malaysian police said.

VX is the world's most potent nerve agent and one of the most dangerous chemical weapons ever manufactured. It's banned under the Chemical Weapons Convention

Arrest warrant issued

Malaysian police also have issued an arrest warrant for an employee of North Korean airline Air Koryo in connection with Kim's death, Malaysian state media reported.

Khalid Abu Bakar, inspector general of Malaysian police, said a warrant was issued for Kim Uk Il, 37, according to Bernama, the state-run news agency. He is wanted for questioning in Kim's death.

Malaysia also has sought the cooperation of Hyon Kwang Song, second secretary at the North Korean Embassy, in relation to the investigation, Bakar said.

The Malaysian deputy prime minister had warned the North Korean ambassador to cooperate with their requests.

"As an ambassador, even if the script comes from sources that he himself knows, he must respect our judicial system, ethics, culture and customs by our country," he said.

North Korean's release

On Friday, Ri Jong Chol -- the only North Korean man held in connection with Kim's death -- was released from custody under heavy police escort on his way to being deported.

Police don't have sufficient evidence to charge Ri, Malaysia's attorney general told CNN on Thursday.

The deputy prime minister said Ri was to fly from Malaysia to Pyongyang, via Beijing, accompanied by two officials from the North Korean Embassy.

Datuk Seri Mustafar Ali, Malaysia's director general of immigration, said Ri has been blacklisted from re-entering the country.

Malaysia's Ministry of Foreign Affairs said Ri's release is proof that the investigation into Kim's death is being "conducted in an impartial, fair and transparent manner, as befits a country that practices the rule of law."