Smoke rises from the Ajil oil field
Smoke rises from the Ajil oil field in Al Hadidiya, south of TikritReuters

The Islamic State (Isis) has lost one of its main sources of revenue, retreating from at least three large oil fields in Iraq due to the military offensive of the Kurdish peshmerga and government forces, according to German media reports.

The jihadist group, which is considered the world's richest terrorist group thanks to 2014 raid on an Iraqi bank, now controls just a single oilfield in the country, the Sueddeutsche Zeitung newspaper reported, citing the BND federal intelligence service.

IS militants set ablaze the two oilfields of Himrin and Ajil north-east of Tikrit in the face of the advancing counteroffensive by Iraqi security forces and Shi'ite and Sunni militia, which eventually wrestled back the city from the jihadists.

"In the eyes of the BND, that is proof that IS [Isis] itself does not believe in a quick recapture (of lost territory)," the newspaper said.

The extremist group is holding control of the northern Qayara oilfield, which has a capacity of just 2,000 barrels per day. That amounts of just 5% of the previous extraction capability. Also, IS lacks the necessary expertise to fully use the oil fields under their control.

The BND concluded that IS "can hardly sell oil anymore" and one of its main sources of income "is under dramatic pressure".

The group's main sources of income originate from taxes, extortion, smuggling of antiquities, kidnapping and oil smuggling.