The Islamic State group has lost control of "at least three large oil fields" in Iraq, depriving the jihadists of a crucial source of income, a German newspaper report said Thursday.

In the face of a large-scale Iraqi counteroffensive, the extremist group now controls just a single oil field in the country, the Sueddeutsche Zeitung said in its Thursday edition, citing the BND federal intelligence services.

Ousted from the strategic northern city of Tikrit by Iraqi security forces and militias just over a week ago -- in Baghdad's biggest victory to date after the militants overran large parts of the country last June -- the jihadists now have only "five percent" of the extraction capabilities they had before, according to the BND report seen by Sueddeutsche Zeitung.

The group had lost "at least three large oil fields", the daily said, adding that satellite images from last month showed the group had set fire to two of them -- the Himrin and Ajil fields -- in the face of the advancing counteroffensive.

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

IS has only held onto the northern Qayara oil field, which has a total output capacity of around just 2,000 barrels a day, according to the German intelligence services.

The report added that IS also lacked the technical expertise to fully exploit the oil fields, including some in Syria, still under its control.

IS "can hardly sell oil anymore", cutting off a significant income source for the group, the newspaper added.

There are no exact figures detailing the jihadist group's finances, but as well as oil revenues IS' income is supplemented by various other activities, including the smuggling of antiques, taxes imposed on local businesses and ransom demands.