Those suicide bomb vests aren’t cheap.

BAGHDAD, July 23 (Reuters) – Islamic State militants seized four small oilfields when they swept through north Iraq last month and are now selling crude oil and gasoline from them to finance their newly declared “caliphate”.

Near the northern city of Mosul, the Islamic State has taken over the Najma and Qayara fields, while further south near Tikrit it overran the Himreen and Ajil fields during its two-day sweep through northern Iraq in mid-June.

The oilfields in Islamic State hands are modest compared to Iraq’s giant fields near Kirkuk and Basra, which are under Kurdish and central government control. Most of the Islamic State-held oil wells – estimated by a Kurdish official to number around 80 – are sealed and not pumping.

But the monopoly over fuel in the territory it has captured gives the Islamic State leverage over other armed Sunni factions who could threaten its dominance in northern Iraq.

Iraqi officials say that in recent weeks the group has transported oil from Qayara to be processed by mobile refineries in Syria into low quality gasoil and gasoline, then brought back for sale in Mosul, a city of 2 million people.