At Raqqa's eastern edge, a handful of Syrian fighters cross a river by foot and car, all the while relaying their coordinates to the U.S.-led coalition so they don't fall victim to friendly fire.

This is their only way into al-Mishlab, the first district the Kurdish and Arab militias have swept into, in what the coalition says will be a long and difficult battle for Raqqa, Islamic State's de facto "capital" in Syria.

The Syrian Democratic Forces (SDF) launched their assault to capture the city this week.