ISIS has released a new video showing captured Syrian soldiers from the Tabqa Air Base in Raqqa Province. They claim to have executed 250 of them, apparently above and beyond the 170 reported killed in the base takeover.
ISIS claimed that many of the soldiers were captured after having fled the air base, and were trying to make their way to Hama, the nearest area still under Syrian government control.
Tabqa was the last Syrian base in Raqqa Province, now entirely under ISIS control. ISIS similarly controls all of the Deir Ezzor Province, as well as parts of several neighboring provinces and virtually the whole of western Iraq.
Mass executions in the wake of territorial gains are common for ISIS, though it is impossible to confirm the figures claimed in their statements, and leads to sometimes wild overstatements of the numbers actually killed in such incidents.