As you know, there are no missiles firing on any Syrian citizens. Article 51 of the United Nations Charter allows the right of self-defence only in cases where a country is under attack as Israel has been for the last sixty two years. A regime like Syria which is not under attack and does not recognise its neighbour's right to exist has no possible claim under international law for the right of self-defence.
15 police officers killed in Colombia helicopter crash (Reuters)
from the article: Assad: Israel leading the Middle East to war