MOSCOW - Russian Foreign Minister Sergei Lavrov has told US Secretary of State John Kerry that more US military support for forces opposed to Syrian President Bashar Assad could stoke violence in the Middle East, the ministry said in a statement on Friday.A US official said on Thursday that President Barack Obama had authorized sending US weapons to Syrian rebels for the first time, after the White House said it had proof the Syrian government had used chemical weapons against opposition forces.During a telephone conversation, Lavrov "stressed that such a step (military support) risks escalating (violence) in the region, while accusations against Damascus of the use of chemical weapons by the United States are not backed up by verified facts," the statement said.