KUALA LUMPUR, Malaysia — Malaysia is protecting its “sovereignty and dignity” by expelling the North Korean ambassador, the prime minister said Monday, as relations between the countries unraveled further over the poisoning of Kim Jong Nam, the estranged half brother of North Korea’s leader.

The bizarre murder case — and the ensuing diplomatic battle — appear to have cost North Korea one of its few friends in the international community.

Just hours after the North Korean ambassador headed to the airport to leave Malaysia, North Korea responded in kind, announcing that it was ordering Malaysia’s envoy out of Pyongyang. But the move was symbolic. Malaysia had already recalled its diplomat shortly after the killing.

In an attack many believe was orchestrated by North Korea, 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.

On Monday, 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 Monday afternoon at the Kuala Lumpur airport, where he told reporters that Malaysia was doing “great harm” to the countries’ relations.

Soon after, North Korea’s official Korean Central News Agency said Malaysia’s ambassador would also be expelled.

Malaysia’s Foreign Ministry spokesman, Raja Nushirwan Zainal Abidin, said North Korea’s decision to expel the Malaysia envoy had been expected.

“This reciprocal action is normal in diplomacy,” he said, adding that the envoy had been recalled two weeks ago for consultations and was still in Kuala Lumpur.

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.