Syrian opposition fighters stormed a northern air defense base near the border with Turkey on Tuesday in their latest offensive against military fortifications, opposition sources said.

More than half of the sprawling compound at Sheikh Suleiman has fallen to rebels as fierce fighting raged at the site, 18 km (11 miles) from the border with Turkey and 30 km northwest of the contested city of Aleppo, rebel sources and opposition campaigners in the area said.