BEIRUT (Reuters) - A U.S.-backed alliance of Syrian militias is widening an offensive against Islamic State near its de facto capital of Raqqa, targeting an area where the group controls a disused air base, a monitoring group and a Kurdish official said on Monday.
The Syria Democratic Forces (SDF), which includes the Kurdish YPG militia, launched an attack against Islamic State-held areas north of Raqqa city last week. The city itself is not a target of the current offensive however, the SDF has said.
In an expansion of the operation, the SDF is now targeting the IS-held area of Tabqa, some 60 km (40 miles), to the west of Raqqa city. IS captured Tabqa air base from government forces in 2014 at the height of its rapid expansion in Iraq and Syria, killing scores of Syrian soldiers there.
The SDF forces are advancing toward Tabqa from Ain Issa, an SDF-controlled town some 70 km (40 miles) to the northeast.
The Tabqa area is important because it links Raqqa city with areas controlled by the group near Aleppo. Syrian government forces backed by Russian air strikes were last year advancing in the direction of Tabqa, after capturing Kweiras air base in Aleppo province, but stopped some 60 km northwest of the town.
The Syrian Observatory for Human Rights, the monitoring group, said Tabqa would be a difficult military target because Islamic State has large stocks of weapons there.
The attacking SDF forces must also cross the Euphrates river to reach Tabqa town, further complicating any assault, Observatory Director Rami Abdulrahman said.
Writing by Tom Perry; Editing by Jon Boyle