"Our air force has taken delivery of at least five fighter planes from Moscow as well as reconnaissance aircraft which allow us to identify targets with great accuracy," the senior official told AFP on condition of anonymity.
The source said the aircraft had arrived on Friday at a military base in Latakia province, the traditional heartland of President Bashar al-Assad's regime.
Moscow has also delivered other "sophisticated military equipment to fight IS," the official said.
"These are defensive and offensive weapons" including "sophisticated arms that target with accuracy and precision-guided missiles," the official said.
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"The Syrian military has started using them in the cities of Deir Ezzor and Raqa, in particular against IS positions," the official said.
Another military source in Latakia told AFP the army had "received Russian reconnaissance planes that will allow Syrian ground and air forces to accurately identify targets."
The deliveries also included "radars and infra-red binoculars," the source said.