US-backed fighters chase IS gunmen near prison in Syria

Officials and activists say Kurdish-led fighters advanced slowly under the cover of U.S.-led coalition air power in Syria’s northeast

BEIRUT -- Kurdish-led fighters advanced slowly Saturday under the cover of U.S.-led coalition air power in Syria's northeast. Intense clashes with Islamic State militants took place around a prison where thousands of extremists were held, officials said.

Fighting broke out Thursday night when IS unleashed its biggest attack in Syria since the fall of its “caliphate” three years ago. More than 100 militants assaulted the main prison holding suspected extremists in the northeastern city of Hassakeh, sparking a battle with U.S.-backed Kurdish fighters that has so far left dozens dead.

Despite their defeat in Syria nearly three years ago, IS sleeper cells have carried out deadly attacks against U.S.-backed fighters of the Kurdish-led Syrian Democratic Forces as well as government forces on the west bank of the Tigris River in eastern Syria.

The group’s territorial control in Syria and Iraq, where they once declared their “caliphate” was crushed by a years-long U.S.-backed campaign. But its fighters continued with sleeper cells that have increasingly killed scores of Iraqis and Syrians in past months.