The United States is warning that a Russian military buildup in Syria could lead to a "confrontation" with the U.S.-led coalition carrying out air strikes against the Islamic State (IS) group.
White House spokesman Josh Earnest said on September 8 that Washington is "concerned by reports that Russia may have deployed additional military personnel and aircraft to Syria."
"If they were to follow through in providing that kind of support, it could be both destabilizing and counterproductive to the interest of the international community," Earnest said.
He said "these steps could lead to greater loss of life [in Syria], they could increase refugee flows and risk confrontation with the counter-[IS] coalition that's operating inside of Syria."
Bulgaria said earlier on September 8 that it has refused a Russian request for two overflight rights for military supply planes to fly to Syria.
The U.S.-led coalition has completed some 50,000 sorties in a little more than one year against IS militants and their assets in Syria and Iraq.