A US fighter jet has shot down a Syrian government plane in Syria's Raqqa province. The US-led coalition on yesterday said it downed the plane after it dropped bombs on American-backed forces fighting ISIL in northern Syria. <br/><br/>Yet, the Syrian army said its jet was on a combat mission against the armed group's fighters near the city of Raqqa, ISIL's de-facto capital in Syria. The incident came as a monitoring group reported the first ground fighting between Syrian government troops and the US-backed alliance of Kurdish and Arab fighters.<br/><br/>The escalation comes as Syria's six-year-old war becomes ever more complex, with US forces and their allies converging on the northern IS bastion of Raqa in close proximity to Russian-backed regime troops.<br/><br/>Further complicating matters, Iran said it launched missile strikes Sunday against terror bases in Syria's northeastern Deir Ezzor province in revenge for deadly attacks<br/>on its capital claimed by IS.<br/><br/>The US-backed Syrian Democratic Forces an alliance of Kurdish and Arab fighters – is battling to oust the jihadists from Raqa, and broke into the IS stronghold city last week.