In international law, there is a principle that is of paramount importance—the principle of non-refoulement (prohibition to return). The principle is applicable to any refugee, asylum-seeker or an alien who needs some form of shelter from the state whose control he/she is under. The non-refoulement principle means that states cannot return aliens to territories where they might be subjected to torture, inhumane or degrading treatment, or where their lives and freedoms might be at risk.
Source: wiktionary