Russia said it has intensified its air campaign in Syria to help President Bashar Assad's forces drive Islamic State militants from Deir el-Zour, a major stronghold for the group, killing an estimated 800 militants across the country this month alone.<br/>'<br/>Col. Gen. Sergei Rudskoi said in Moscow that Russian jets are now making 60 to 70 flights a day to target militants heading from other areas to join the fight in the eastern city. <br/><br/>He says Syrian troops are meanwhile advancing from three directions to encircle Deir el-Zour. Rudskoi said militants fleeing US-backed offensives in the Iraqi city of Mosul and the Syrian city of Raqqa have poured into Deir el-Zour in recent months.<br/>'<br/>Russia has waged an air campaign in Syria since September 2015 aimed at helping Assad's forces defeat IS as well as Syrian rebel groups. <br/>'<br/>'''''''<br/>