At least 47 fighters were killed in clashes between ISIS and Syrian insurgents, a monitor said on Saturday, in an area where the United States and Turkey are planning to open a new front against the terrorists.The renewed fighting raged on Friday around the rebel-held town of Marea, 20 km (12 miles) from the Turkish border, the Britain-based Syrian Observatory for Human Rights said.The area falls within a "safe zone" Turkey said last month it would set up in northern Syria to help keep ISIS at bay.