The principle of non-refoulement

Humanitarian aid

 Non-refoulement is a principle in international law, specifically refugee law, that concerns the protection of refugees from being returned to places where their lives or freedoms could be threatened. Unlike political asylum, which applies to those who can prove a well-grounded fear of persecution based on membership in a social group or class of persons, non-refoulement refers to the generic repatriation of people, generally refugees into war zones and other disaster areas.
Non-refoulement is a jus cogens of international law that forbids the expulsion of a refugee into an area where the person might be again subjected to persecution.

Codified within the 1951 Geneva Convention and 1967 Protocol, the principle of non-refoulement arises out of an international collective memory of the failure of nations during World War II to provide safehaven to refugees fleeing certain genocide at the hands of the Nazi regime. Today the principle of non-refoulement ostensibly protects recognized refugees and asylum seekers from being expelled from countries that are signatories to the 1951 Convention or 1967 Protocol. This has however not prevented certain signatory countries from skirting the international law principle and repatriating or expelling bona fide refugees into the hands of potential persecutors. Tanzania's actions during the 1994 genocide in Rwanda have been alleged to have violated the nonrefoulement principle. During the height of the crisis when the refugee flows rose to the level of a "mass exodus," the Tanzanian government closed its borders to a group of more than 50,000 Rwandan refugees who were fleeing genocidal violence. In 1996, before Rwanda had reached an appropriate level of stability, around 500,000 refugees were returned to Rwanda from Zaire.

One of the grey areas of law most hotly debated within signatory circles is the interpretation of Article 33. Interdiction of potential refugee transporting vessels on the highseas has been a common practice by the U.S. government in particular, raising the question of whether Article 33 requires a refugee to be within a country or simply within the power of a country to trigger the right against refoulement.
 

Since 1951, 140 states have signed the Convention, officially recognizing the binding principle of non-refoulement expressed therein.
 

 Wikipedia: The principle of non-refoulement