A US jet has shot down an Iranian-made drone operated by forces backing the Syrian government in the south of the country. <br/><br/>The drone was thought to be armed and threatening US-led coalition troops on the ground. But Russian Deputy Foreign Minister Sergei Ryabkov said the action amounted to complicity with terrorism. <br/><br/>The incident comes after the US shot down a Syrian fighter plane on Sunday and another drone earlier this month. <br/><br/>According to a US military statement the F-15 plane downed the drone north-east of Tanf, an outpost of the US-led coalition.<br/><br/>In another development, the US military announced officially that coalition forces had killed the top cleric of so-called Islamic State Turki al-Binali, in an air strike in Syria last month. IS supporters have also reported his death.