Russia has started flying drones over Syria in what appears to be its first aerial surveillance operations over the war-ravaged country, NBC News reports.
U.S. defense officials told NBC News that although there was no indication Russia had yet conducted combat missions using fighter jets and attack helicopters, they said they expected such operations to start soon.
Moscow has already sent in four SUKHOI attack fighter jets, four HIND attack assault helicopters, four HIP transport helicopters, along with tanks and artillery, the officials said.
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In addition, it has now flown in large quantities of air-to-ground missiles, high-caliber ammunition for attack-jet machine guns and aircraft fuel, the officials added.
According to one senior official: "They didn't fly all those attack aircraft in there to leave them sit on the runway."
The Russian Ministry of Defense was not available for comment when contacted by NBC News.
Russia, which supports the regime of Syrian President Bashar Assad, has over the past two weeks been building a military presence near the Syrian port city of Latakia.
The U.S. supports rebels fighting Assad, but both Washington and Moscow have a common enemy in ISIS, which has more recently joined the conflict and been the target of U.S.-led airstrikes.