After thousands of Iraqi soldiers fled the Islamic State offensive, Shiite militias and Kurdish fighters have emerged as a key line of defence against the militants, who have threatened to march on Baghdad.
Kurdish forces poured in reinforcements, including special forces, to the town of Zumar this weekend to battle Islamic State fighters who had arrived from three directions, residents said. The militants later hoisted their black flag over buildings in Zumar, a ritual that has in the past been followed by the mass execution of captured opponents and the violent imposition of an ideology that even al-Qaeda finds excessive. The Islamic State later also seized the town of Sinjar, where residents had fled after Kurdish fighters put up little resistance.
Islamic State has stalled in its drive to reach Baghdad, halting just north of the town of Samarra, 100 km north of the capital.
The Islamic State in Iraq and the Levant (ISIL) changed its name earlier this year and declared a caliphate in parts of Iraq and Syria. The group has already seized four oil fields, which help fund its operations.
The group has been trying to consolidate its gains, setting its sights on strategic towns near oil fields, as well as border crossings with Syria so that it can move easily back and forth and transport supplies. It has capitalised on sectarian tensions and disenchantment with Iraqs Shiite Prime Minister Nuri al-Maliki.
Critics describe Maliki as an authoritarian leader who has put allies from the Shiite majority in key military and government positions at the expense of Sunnis, driving a growing number of the religious minority in Iraq to support the Islamic State and other insurgents. He is also at odds with the Kurds.
The Kurds have long dreamed of their own independent state, an aspiration that has angered Maliki. After the Islamic State arrived, Kurdish forces seized two oil fields in northern Iraq and took over operations from a state-run oil company.
In another move certain to infuriate the Baghdad government, the Kurdish region is pressing Washington for sophisticated weapons it says Kurdish fighters need to push back the Islamist militants, Kurdish and US officials said. But Maliki needs the Kurds to help defend his government.
An official in the Northern Oil Company said Islamic State fighters had taken control of the Ain Zalah oil field and two other undeveloped fields Batma and Sufaiya.
On its website on Sunday, Islamic State said its fighters had killed scores of Kurdish fighters and then had taken over Zumar and 12 villages. Hundreds fled and a huge number of weapons and munitions and the brothers control many areas... The fighters arrived in the border triangle between Iraq, Syria and Turkey, it said.