FILE - This frame grab from a March 6, 2017 video provided by the Syria Democratic Forces (SDF), shows fighters from the SDF opening fire on a position of the Islamic State group in the countryside east of Raqqa, Syria. As the American –backed SDF fighters bear down on Raqqa, the militants have trapped the city’s estimated 300,000 residents to use as human shields, ringing the city with land mines to prevent escape.