A U.S.-backed alliance of Syrian Kurds and Arab rebel groups advanced towards a dam in northern Syria held by Islamic State fighters on Thursday, in an assault aimed at capturing the militants’ stronghold of Raqqa, rebels and a monitor said.

They said the push by fighters of the Democratic Forces of Syria, which includes the powerful Kurdish YPG militia and an Arab tribal alliance, had brought them within 20 km of the Tishreen Dam, one of three major dams on the Euphrates River.

Further south of the dam that still supplies power to large areas in northern Syria is the even larger Baath Dam. Its power plant, under militant control, feeds much of the territory under Islamic State and is 22 km (15 miles) upstream from Raqqa. […]