Iran is doubling the price of its oil going to Syria to a market rate of over $70 per barrel and now refuses to ship oil to Damascus on credit, demanding payment in advance, sources with knowledge of the matter told The Wall Street Journal on Sunday. The new restrictions on deliveries of Iranian oil—which accounts for more than half of Syria’s oil consumption—are further straining the already struggling Syrian economy. The fuel shortages are the worst since the beginning of the civil war in Syria a decade ago, analysts…