KUALA LUMPUR - Malaysian Prime Minister Najib Razak said on Tuesday that he had instructed police to ban all citizens from the Democratic People's Republic of Korea from leaving the country after Pyongyang announced a similar ban.

The prime minister also urged the DPRK to immediately allow all Malaysians to leave to "avoid any further escalation".

Describing the DPRK's exit ban as an "abhorrent act, effectively holding our citizens hostage", Najib said it was in total disregard of all international law and diplomatic norms.

"Protecting our citizens is my first priority, and we will not hesitate to take all measures necessary when they are threatened," he said, adding that he also instructed police to prevent all DPRK citizens in Malaysia from leaving the country until "we are assured of the safety and security of all Malaysians in the DPRK".

In tit-for-tat moves, Malaysia and the DPRK have expelled each other's ambassador as an investigation into the death of a DPRK man strained bilateral relations.

Earlier in the day, Deputy Prime Minister Ahmad Zahid Hamidi said the Malaysian government has banned all DPRK embassy staff from leaving the country.

The measure, which will be enforced by the Home Ministry, was "in response to the measures taken by the Foreign Ministry of the DPRK", Zahid told reporters while attending a parliament session, adding Malaysia was forced to take the measure because the DPRK had gone beyond diplomatic etiquette.

Malaysian police and health authorities said a DPRK man was killed by the nerve agent VX, a lethal chemical weapon banned by the UN, at the Kuala Lumpur airport on Feb 13. Two female suspects who smeared the chemical on his face have been indicted on murder charges while four DPRK suspects had fled Malaysia.

'Not cooperating'

The police also wanted to question three men in connection with the case, including a second secretary at the DPRK embassy in Kuala Lumpur and an Air Koyro employee. While attending a meeting on drug enforcement, Malaysian police chief Khalid Abu Bakar said police believed the three were hiding in the DPRK embassy.

He also said the DPRK authorities were not cooperating with the Malaysian side in the investigation and refused to hand over the four fleeing suspects.

Khalid said the police would give the bereaved family a little bit more time to come to identify the body of the DPRK man. "We are confident we will get the DNA samples," he said.