According to the Sankei, it says the US military have shot down a Syrian warplane on June 18. The CNN says this attack is the first time since the Syrian civil war happened in 2011. Additionally, US army emphasized that this shot down was after Syrian regime of Bashar al-Assad attacked the north-central Syria town of Ja’Din, which was controlled by the SDF. Obviously, the attack of the USA is legitimate, as it refers to the “In accordance with rules of engagement”, and “in collective self-defense of coalition-partnered forces”. However, the Syrian Army has strongly criticized the US for their behavior, as the state-owned media in Syria reported that they had lost the pilot of the warplane. For instance, it shows the real shape of a nation, which assist the terrorism. Consequently, it is undeniable for this attack to be a trigger to worsen the relationship between the USA and Syrian army even they have a common enemy. Furthermore, it is concerned that the Islamic state might change their strategy, as last attack showed the disorder of the USA.

http://edition.cnn.com/2017/06/18/middleeast/syrian-warplane-shot-down-coalition/index.html