Kirkuk pipeline exports were briefly offline after IS militants bombed high-voltage power lines – one of a dozen insurgent attacks to hit northern Iraq in the past week.

IS militants are still stealing oil from wellheads in the mountains of Salahaddin province - in the process, unleashing a flood of oil that flows for miles.

Investigators suspect members of the Badr Organization paramilitary group conducted a small but steady smuggling operation at a makeshift military base south of Kirkuk.

In territory that was ostensibly liberated two years ago, security forces, civilians, and energy infrastructure have become regular targets of an intensifying IS guerrilla war.