KUALA LUMPUR -Malaysia and North Korea have barred each other's citizens from leaving, effectively holding them hostage amid a worsening diplomatic row over the killing of Kim Jong Nam, the estranged half-brother of North Korean leader Kim Jong Un.

"I condemn in the strongest possible terms North Korea's decision to prevent Malaysian citizens from leaving the country," Malaysian Prime Minister Najib Razak said in a statement on Tuesday (March 7).

"This abhorrent act, effectively holding our citizens hostage, is in total disregard of all international law and diplomatic norms," he said. "As a peace-loving nation, Malaysia is committed to maintaining friendly relations with all countries. However, protecting our citizens is my first priority, and we will not hesitate to take all measures necessary when they are threatened."

North Korea's foreign ministry said on Tuesday that all Malaysia citizens in the country "will be temporarily prohibited from leaving the country until the incident that happened in Malaysia is properly solved,” the official Korea Central News Agency (KCNA) reported.

The ministry said Malaysian diplomats and nationals in North Korea would be allowed to conduct business and live normally while the travel ban is in place.

It also expressed hopes that the Malaysian government would resolve the issue in a “fair and timely manner based on goodwill”, according to KCNA.

In a tit-for-tat move, the Malaysian prime minister said: "I have also instructed the Inspector General of Police to prevent all North Korean citizens in Malaysia from leaving the country until we are assured of the safety and security of all Malaysians in North Korea".

"Our hope is for a swift resolution. I call upon the North Korean leadership to immediately allow our citizens to leave to avoid any further escalation," Najib said, adding that he had summoned an emergency meeting of the National Security Council.

Malaysian police sealed off the North Korean embassy in Kuala Lumpur to prevent the North Korean diplomats and staff from leaving the premises. Inspector General of Police Khalid Abu Bakar said on Tuesday that he believed three North Koreans linked to the killing of Kim Jong Nam are inside the embassy.

Deputy Prime Minister Ahmad Zahid Hamidi said "we do not want to react but this is what needs to be done when a country with diplomatic relations with Malaysia acts outside diplomatic norms."

"They have manipulated the murder case and we want to send a clear signal not to point fingers and belittle us as a sovereign state that has conducted investigations professionally," said Mr Zahid, who is also home minister.

Deputy Foreign Minister Reezak Marican told reporters there are 11 Malaysians in North Korea - three of them working at the Malaysian embassy, two are working for the United Nations, and the rest are their family members.

There are 14 North Korean diplomats in Malaysia, based on a foreign ministry list. Reuters reported that hundreds of North Koreans are believed to be in the country, most of them students and workers.

At least 170 North Koreans are believed to be working in Sarawak alone, working mainly in coal mining, bridge construction and hydroelectric dam projects, the New Straits Times reported. The Sarawak government said on Tuesday it will discuss with Malaysia's home and foreign ministries the status of the North Korean workers in the state.

Malaysia and North Korea had strong relations for years, but ties have been strained in recent weeks by the killing of Kim Jong Nam by two women using the deadly VX nerve agent.

South Korea has blamed North Korea for the killing, and Malaysian police have sought several North Koreans for questioning. They detained one North Korean man for two weeks but had to release him for lack of evidence.

Pyongyang has yet to confirm the dead man’s identity but has denounced the Malaysian investigation as an attempt to smear it.

Malaysia expelled the North Korean ambassador last Saturday and he left the country on Monday. Pyongyang retaliated late on Monday by expelling the Malaysian ambassador, who had already been recalled by the Malaysian government for consultations.