WASHINGTON/DAMASCUS - Russia has started flying unmanned aircraft over Syria in what appears to be surveillance operations over the country, adding to its military buildup.
US officials, who spoke to Reuters on condition of anonymity, could not immediately say how many Russian drones were involved in the surveillance missions or the scope of the flights.
The start of Russian drone flights underscored the risks of US-led coalition aircraft and Russian flights operating in Syria's limited airspace
The officials were not able to confirm whether the drones were armed, or how many missions have been flown to date.
The Pentagon declined comment at a news briefing when asked about the Reuters report on Russian drones, saying it could not discuss intelligence matters. But it said the US Department of Defense was "keenly aware" of what was happening on the ground in Syria.
The White House acknowledged that Moscow's intentions were unclear and that the prospect of deepening Russian military backing for Syrian President Bashar al-Assad was troubling.
"We've made clear both in public and in private that doubling down on supporting Assad is a losing bet," said White House spokesman Josh Earnest.
Reuters quoted unnamed US officials as saying that the number of fixed-wing, piloted Russian aircraft stationed at the air base near Latakia, an Assad stronghold, had also grown dramatically in recent days.
That included Russia's positioning of a dozen "Fencer" advanced-attack aircraft and a dozen "Frogfoot" jets, used for close air support. Those were in addition to Russia's first deployment of fighter jets last week.
Russia has over 25 fighter and attack aircraft, 15 helicopters, nine tanks, three surface-to-air missile systems and at least 500 personnel on the ground in Syria, CNN quoted US officials as saying.
Defense Secretary Ashton Carter spoke with Russian Defense Minister Sergei Shoigu on Friday regarding the escalating Russian posture.
The US opposes Russia's policy of bolstering Syrian President Bashar al-Assad. The US has said Assad must leave office for the civil war to be resolved.
"We are keenly aware of what is happening there," Pentagon spokesman Capt. Jeff Davis told reporters Monday. "We continue to believe that anything that's done in support of the Assad regime, particularly militarily, is counter-productive and risks worsening an already bad situation."
Meanwhile, Russia and Iran have stepped up coordination inside Syria to safeguard President Assad's control over his coastal stronghold, creating a new complication for Washington, the WSJ reported.
Senior Russian and Iranian diplomats, generals and strategists have held a string of high-level talks in Moscow in recent months to discuss Assad's defense and the Kremlin's military buildup in Syria, it quoted US and Middle East officials as saying.