The Malaysian PM has accused North Korea of "effectively holding our citizens hostage"
North Korea has barred Malaysians from leaving the country - triggering tit-for-tat action by Malaysia.
It marks a major escalation of the ongoing diplomatic row between the two countries, following the killing of the North Korean leader's half-brother Kim Jong-Nam at Kuala Lumpur airport last month.
Two women - one Indonesian and one Vietnamese - have been charged with murder after police said they smeared Mr Kim's face with VX - a banned nerve agent considered a weapon of mass destruction.
Police in Kuala Lumpur investigating the murder have sealed off the North Korean embassy, amid suspicions that up to three suspects are hiding inside.
Pyongyang has rejected the claim that VX killed Mr Kim, claiming he probably died from a heart attack.
North Korean citizens could previously travel to Malaysia visa-free, but that allowance was rescinded last week.
Yesterday's move by North Korea to bar Malaysian citizens from leaving the country sparked condemnation from senior Malaysian officials.
In a statement posted on Facebook, Malaysian prime minister Najib Razak said: "I condemn in the strongest possible terms North Korea's decision to prevent Malaysian citizens from leaving the country. This abhorrent act, effectively holding our citizens hostage, is in total disregard of all international law and diplomatic norms.
He added he had "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".
It was initially believed that only North Korean diplomatic staff would be banned from leaving Malaysia.
According to BBC, officials believe there are currently around 11 Malaysian citizens - mostly diplomats - in North Korea.
In contrast, it is thought that around 1,000 North Koreans are currently in Malaysia.
Additional reporting by IRN