Islamist rebels have been advancing through large swathes of the country's north-west in the past week, threatening the rule of Syria's long-time president, Bashar Al-Assad.

Syrian opposition forces have taken control of much of the country’s second-largest city Aleppo after a lightning advance that killed dozens of government soldiers in a major challenge to President Bashar al-Assad.

The surprise offensive on Aleppo by Syrian rebel groups has left the US in the difficult position of not fully supporting either side while also maintaining a force posture of nearly 1,000 troops in Syria as part of the ongoing mission to fight ISIS.