The Islamic State group warned Monday it would seek to further expand into autonomous Kurdish territory after claiming key towns and areas over the past 48 hours.

"Islamic State brigades have now reached the border triangle between Iraq, Syria and Turkey. May God Almighty allow his mujahideen to liberate the whole region," it said in a statement.

The jihadist group listed the gains achieved over the weekend in what was its most significant territorial push since first sweeping across Iraq nearly two months ago.

It seized the large town of Sinjar on Sunday, as well as two others in the same area. It took the town of Zumar the previous day and is now threatening Mosul dam, the country's largest.

"The mujahideen (holy fighters) conquered several areas controlled by secular Kurdish gangs and militias," said the statement, issued by IS' branch in the northwestern Iraqi province of Nineveh.

"In a day-long series of battles involving a variety of weapons... the apostate enemies were humiliated, dozens were killed and wounded and hundreds fled."

The Kurdish government has not provided casualty figures nor commented on reports that several Kurdish peshmerga fighters were captured.

The areas IS fighters took were regions the peshmerga moved into in the initial chaos that saw government soldiers retreat in the face of the jihadist offensive launched on June 9.

The latest fighting in Nineveh province means that the peshmerga have largely pulled back to the old borders of their autonomous region.

It also allows the Islamic State's men to move easily between Iraq's second city of Mosul, which they overran on June 10, and the Syrian border.