SEOUL, South Korea >> The bitter diplomatic dispute between North Korea and Malaysia over the poisoning death of leader Kim Jong Un’s estranged half-brother escalated dramatically today, with Pyongyang saying it had banned Malaysians from leaving North Korea.

That was followed quickly by Malaysia saying North Korean embassy staff were barred from leaving its country. Malaysia had already expelled the North Korean ambassador on Monday.

The North’s Foreign Ministry told the Malaysian Embassy in Pyongyang that it would temporarily ban the exit of Malaysian citizens now in the North, according to the official Korean Central News Agency.

It said the exit ban will be valid “until the safety of the diplomats and citizens of (North Korea) in Malaysia is fully guaranteed through the fair settlement of the case that occurred in Malaysia.”

Malaysia is pursuing several North Korean suspects allegedly involved in the killing, including a diplomat at the North’s Embassy in Kuala Lumpur. Malaysia has not accused the North of being behind the killing of Kim Jong Nam at Kuala Lumpur’s airport three weeks ago, but South Korea has.

Malaysian Deputy Foreign Minister Reezal Marican told reporters at parliament that there are 11 Malaysians in North Korea: Three working at the Malaysian Embassy, two United Nations workers and six family members.

The North said Malaysian diplomats and citizens “may work and live normally under the same conditions and circumstances as before” during the period of the temporary exit ban.

It also said that the Malaysian ambassador would be expelled, although he has already been recalled to Malaysia.

Kim Jong Nam died less than 20 minutes after two women wiped VX nerve agent on his face at Kuala Lumpur airport on Feb. 13, authorities say. The women, one from Vietnam and one from Indonesia, have been charged with murder.

North Korea has denied any role in the killing and accused Malaysia of conspiring with its enemies. North Korean Ambassador Kang Chol rejected a Malaysian autopsy that found Kim was killed with VX, a banned chemical weapon.

Today, Malaysian Prime Minister Najib Razak said the decision to expel Kang sent a clear message.

“It means that we are firm in defending our sovereignty and dignity,” Najib said. “Don’t ever insult our country and don’t try to cause disruptions here.”

Malaysian authorities declared Kang “persona non grata” on Saturday and gave him two days to leave the country. He arrived late this afternoon at the Kuala Lumpur airport, where he told reporters that Malaysia was doing “great harm” to the countries’ relations.

Malaysia’s finding that VX killed Kim boosted speculation that North Korea was behind the attack. Experts say the oily poison was almost certainly produced in a sophisticated state weapons laboratory, and North Korea is widely believed to possess large quantities of chemical weapons, including VX.

North Korea is trying to retrieve Kim’s body, but has not acknowledged that the victim is Kim Jong Un’s half brother, as Malaysian government officials have confirmed.

Ri Tong Il, a former North Korean deputy ambassador to the United Nations, has said Kim probably died of a heart attack because he suffered from heart disease, diabetes and high blood pressure. Health Minister Subramaniam Sathasivam said pathologists have ruled that out.

The two women accused of poisoning Kim say they were duped into thinking they were taking part in a harmless prank.

Malaysia is looking for seven North Korean suspects, four of whom are believed to have left the country on the day of the killing. The three others, including an official at the North Korean Embassy and an employee of Air Koryo, North Korea’s national carrier, are believed to still be in Malaysia.