With the beginning of Syrian crisis in 2011, the opponent governments of Syrian regime tried in different ways to undermine and eventually overthrow the popular Syrian government. In this regard, the most important effort have been sending weapons, specially chemical weapons, to terrorist groups, particularly ISIS that has been intensified since the chemical attacks by terrorists in August 2013 in Syria. Obviously the entities in charge of arms sending have not been ordinary citizens in spite of some evidence, this article tries to answer the following questions by adopting a cross-sectional approach and citing the binding principles of international law and authentic scientific sites .Which foreign governments take part in arms support of terrorists in Syria? How the international responsibility for supporting terrorist by means arms supply in Syria could be assigned to them? The results of this study suggest that according to explicit international law prohibition on supporting terrorism in a variety of ways and jus cogens like non-intervention, non-aggression, neutrality in conflicts in international law, those who provide terrorist groups with external financial, weaponry and media support in Syria, can be assumed responsible for terrorist acts. So, the international responsibility of Western and Arab states and certain international organizations is proved in Syria
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