Col. Gen. Sergei Rudskoi said 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. He says Syrian troops are meanwhile advancing from three directions to encircle Deir el-Zour.
Syrian government forces control around half the city and a nearby air base, both of which are besieged by the militants. 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.
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. This month alone, Russian warplanes have flown 990 missions, destroying 40 armored vehicles, more than 100 trucks and killing about 800 militants, Rudskoi said.
Those casualties include more than 200 militants killed in a recent raid on an IS convoy heading toward Deir El-Zour, according to the Russian Defense Ministry.