A Kurdish militia that has been fighting Islamic State in Syria with help from U.S.-led air strikes has joined forces with Arab groups in an alliance announced on Monday that may be a prelude to an attack on the jihadists' base of operations in Raqqa.
The alliance calling itself the Democratic Forces of Syria includes the Kurdish YPG militia and Syrian Arab groups, some of which fought alongside it in a campaign that drove Islamic State from wide areas of northern Syria earlier this year.