"The principle of non-refoulement is a cornerstone of international law. This principle is set out in the 1951 Refugee Convention, article 33 (1) of which states that “No Contracting State shall expel or return ("refouler") a refugee in any manner whatsoever to the frontiers of territories where his life or freedom would be threatened on account of his or her race, religion, nationality, membership of a particular social group or political opinion”.1 The convention does list a number of grounds on which a person may be refouled. According to article 33 (2), the ban on forcibly returning refugees to a country where they may face persecution does not apply to a refugee “whom there are reasonable grounds for regarding as a danger to the security of the country in which he is or who, having been convicted by a final judgment of a particularly serious crime, constitutes a danger to the community of that country”. However, this provision is only valid under highly exceptional circumstances: for it to be applicable it must be proved that there is a direct link between the presence of a refugee in the territory of a particular country and a national security threat to that country."
http://www.ihf-hr.org/viewbinary/viewdocument.php?doc_id=673...

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Note added at 8 mins (2010-05-24 18:43:30 GMT)
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...torture, death, or certain other forms of oppression
(wouldn't fit in answer field)