The jihadist attack launched yesterday on the Zumar area, northwest of Mosul, Iraq's second city, drew Kurdish forces deeper into a conflict which has raged for close to two months.
The jihadists "attacked a peshmerga post in Zumar and a fierce battle erupted," said an official in the Patriotic Union of Kurdistan (PUK), one of Iraq's two main Kurdish parties.
He told AFP that 14 peshmerga fighters were killed, a toll confirmed by a senior officer in the Kurdish force.
The PUK official said the peshmerga killed "around 100" IS fighters and captured 38.
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The officials said the peshmerga fought off the jihadists, only to withdraw later today, allowing IS fighters to take control of the area, which includes the Ain Zalah and Batma fields.
"The two oilfields are now under IS control," an official with the North Oil Co told AFP, adding the fields have a combined capacity of 20,000 barrels per day.
He said the site also includes a small power plant.
"Zumar and the surrounding region fell to Daash, after they pulled out today," Gayath Surchi, another PUK official, told reporters, using the former Arabic acronym for the jihadists.
Government forces retreated in the face of the onslaught, with peshmerga troops filling the vacuum and seizing long-coveted areas disputed by the Kurds and Baghdad, including the oilfields.
The peshmerga are widely perceived as Iraq's best organised and most efficient military force but the autonomous Kurdish region in the north has been cash-strapped and its troops stretched.
According to a senior official, a Kurdish delegation is currently in the United States to demand military support.