The Syrian military has recently started using new types of air and ground weapons supplied by Russia, a Syrian military source told Reuters on Thursday, underlining growing Russian support to Damascus that is alarming the United States.

"The weapons are highly effective and very accurate, and hit targets precisely," the source said in response to a question about Russian support. "We can say they are all types of weapons — be it air or ground."

The source said the army had been trained in the use of the weapons in recent months and was now deploying them, declining to give further details other than saying they were "new types.