In a medical clinic packed with injured Syrian rebels, 23-year-old Mohammed Hadhoud lies waiting for an operation to remove a machine-gun bullet lodged in his spine. His family cannot afford the bill, and the moderate Islamist brigade he fights with has refused to fully cover the cost.

Down the corridor, two fighters for al-Qaida-linked Jabhat al-Nusra rest up, their treatment paid for. One reaches from under his pillow to show the $100 he has been given in spending money.

"In case we need anything extra," he says.