BEIRUT - The US-backed Syria Democratic Forces alliance has crossed into Deir al-Zor province for the first time, as part of a US-backed offensive against Islamic State, a Kurdish military source said on Tuesday.The advance is part of an operation to encircle and ultimately capture the ultra-hardline group's de facto Syrian capital of Raqqa in the north of the country.The SDF, which consists of Kurdish and Arab fighters, had entered the northern part of Deir al-Zor province and captured a number of villages from Islamic State militants, the Kurdish military source told Reuters.
