Kurds advance deeper into ISIL territory within 40 miles of Raqqa

Reuters:

Kurdish-led forces advanced on Monday deep into territory in Syria held by Islamic State, showing new momentum after they unexpectedly swiftly seized a border crossing from the jihadists last week.

The Kurds, aided by U.S.-led air strikes and smaller Syrian rebel groups, had pushed to within 7 km (4 miles) of Ain Issa, a town 50 km (30 miles) north of Islamic State's de facto capital Raqqa city, said Redur Xelil, spokesman for the Kurdish forces.

The rapid advance into Raqqa province has defied expectations of a protracted battle between the Kurdish YPG group and Islamic State fighters, who waged a four-month battle for the border town of Kobani, where the Kurds finally defeated the jihadists in January.

Raqqa is the main seat of power in Syria for Islamic State, the group also known as ISIS or ISIL, which has proclaimed a caliphate to rule over all Muslims from territory it controls in both Syria and Iraq.

The United States has been leading an air campaign against the group in both countries since last year. The Kurds have been the most important partner so far for the U.S.-led campaign in Syria, where Washington has far fewer allies on the ground than in Iraq.
...

 The advance has apparently caught the ISIL forces by surprise.  They had probably been expected attacks in Mosul and Ramadi in Iraq.  Instead, the Kurds with the help of US air power are coming in their back door.  The advance may give the US air campaign an opportunity if ISIL starts pulling its forces out of Iraq to defend Raqqa.  They would be in open desert and vulnerable to attacks from US A-10's if Obama frees them up for use.