US and Western diplomats scrambled on Saturday to cobble together a diplomatic strategy to end the war in Syria, after the latest humiliating blow to their military plan. Secretary of State John Kerry and his European counterparts reached out to traditional foe Iran on the sidelines of the UN General Assembly in New York, AFP reports.

Iran and Russia back Syrian strongman Bashar al-Assad, whom Washington sees as the instigator of the civil war that left half his country in the hands of the "Islamic State" (ISIS) terrorist group.

Unwilling to countenance a peace process that would leave Assad in power after he alienated or killed so many of his people, the US has backed small "moderate" rebel groups. But that strategy appeared in tatters on Saturday after the Pentagon admitted the latest US-trained fighters to cross into Syria had given a quarter of their gear to Al-Qaeda.