Based on currently available information, Malaysia and North Korea’s diplomatic ties spanning four decades was gravely damaged when Kim Jong Nam, the estranged brother of Kim Jong-un was assassinated at KLIA on 13th February 2017. Tensions between the two countries escalated when the North Korea ambassador, Kang Chol, criticized the handling of the case by Malaysian authorities, even going as far as to accuse Malaysia of being untrustworthy and colluding with other nations to defame North Korea. 
As a result, he was declared a persona non grata—likely the first of which has ever happened to a diplomat stationed in Malaysia—and therefore, expelled from the country. Persona non grata, which is provided for in Article 9 of the Vienna Convention of Diplomatic Relations 1961, an international convention to which both Malaysia and North Korea are parties to, allows a receiving state to “notify the sending State that the head of the mission or any member of the diplomatic staff of the mission ... is not acceptable.” At which point, “the sending State shall, as appropriate, either recall the person concerned or terminate his functions with the mission.” If the sending State refuses or fails within a reasonable period to carry out its obligations to recall the person, the receiving State may “refuse to recognize the person concerned as a member of the mission.” 
In other words, the foreign diplomat would no longer be welcomed in the receiving state, nor would they continue to enjoy diplomatic immunity under the Vienna Convention. Declaring a diplomatic staff as persona non grata could be considered to be one of the harshest diplomatic measures a state can take against another state.
Not surprisingly, North Korea retaliated by similarly declaring Malaysia’s ambassador, Mohamad Nizan Mohammad, a persona non grata. Soon after, North Korea decided to impose a travel restriction on Malaysians who are in their country, from leaving North Korea. In retaliation, Malaysia has decided to do the same shortly after the decision was made to North Koreans who are currently in this country.
The Malaysian Prime Minister, Najib Razak, in announcing the retaliatory travel ban, released a statement stating that North Korea’s act of holding Malaysian citizens as “hostages”  is in “total disregard of all international law and diplomatic norms.”  However, this begs the question, is the decision to ban foreign citizens from leaving one's country (be it North Korea or Malaysia) a breach of human rights and/or in compliance with international law?
This article aims to study the relevant treaties under international law with regards to the travel ban and to determine if any breach of international law was committed by both Malaysia and North Korea.