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 […]