How Involved is the US in the Manbij Campaign?

Since the first of June the Syrian Democratic Forces (SDF) and the Peoples' Protection Units (YPG) have made major advances into the so-calleed Manbij Pocket along the Syrian-Turkish border, occupying hundreds of square kilometers west of the Euphrates and threatening to cut off one of the Islamic State's remaining outlets to the Turkish border.

Though the Manbij campaign has received less attention than the advance on Falluja i,n Iraq, it is a major success for US-backed forces. In fact there is reason to believe that US Special Forces are embedded with and possibly directing the advance.

Although about 60% of the SDF consist of YPG fighters. the US has sought to emphasize the Arab components in the SDF, in order to persuade Turkey that it is not primarily a Kurdish force advancing along its border. The SDF also includes Arab groups as well as Assyrian, Turkmen, Circassian and other minority groups. It's been reported that the YPG is leading the advance and capturing territory, and then handing control over to non-Kurdish forces.

The SDF says it is refraining from entering Manbij city to avoid civilian casualties,  but appears intent on cutting the routes from Manbij to the Turkish border.