The jihadist Islamic State claimed the capture of Iraq’s biggest dam, an oilfield, and three towns on Sunday in their first major defeat of Kurdish forces since a June offensive.

The Islamic State said it seized the Mosul Dam and the Ain Zalah oil field, adding to four others already under their control.

Pro-Kurdish social media accounts have disputed the reports of defeat.

If true, the reports of the Islamic State’s victories point to its strength not only versus the central Government in Baghdad but also the forces of Iraqi Kurdistan.

In mid-June, the Islamic State was part of an insurgency that captured Iraq’s second city Mosul and Tikrit, advancing on Baghdad. Seeking to secure their territory, Kurdish peshmerga moved into the oil-rich city of Kirkuk in northern Iraq.

This weekend Islamic State fighters attacked the Zumar from three directions in pick-up trucks mounted with weapons, confronting Kurdish forces who had moved reinforcements into the town.

The Islamic State later claimed the capture of Sinjar with little resistance. The jihadists posted a picture of a masked fighter holding up a pistol and sitting at the abandoned desk of the Mayor of Sinjar.

“Hundreds (of Kurdish fighters) fled leaving vehicles and a huge number of weapons and munitions and the brothers control many areas,” the Islamic State said.