In a development demonstrating the perils of journeying in the war-wracked country, at least 17 people -- most of them rebels -- died in a car bomb blast at an opposition checkpoint in northern Aleppo province on Thursday, a monitor said.The blast hit near the town of Azaz close to the border with Turkey, the Britain-based Syrian Observatory for Human Rights said, adding that 14 of the dead were rebel fighters. It said the toll could rise.