Iraq's Prime Minister Nouri al-Maliki has called upon his country's armed forces to help Kurdish forces battle a Sunni militant offensive in northern Iraq that has caused tens of thousands of people from the minority Yazidi community to flee their homes.

Iraq's military spokesman Lt. Gen. Qassim al-Moussawi said Monday that al-Maliki has commanded the air force to provide aerial support to the Kurds in the first sign of co-operation between the two militaries since Iraq's second largest city, Mosul, was captured by the militants on June 10.

Iraq is facing its worst crisis since the 2006 civil war when the Islamic State group captured large swaths of land straddling the Syria-Iraq border with the goal of establishing a self-styled caliphate.

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The militant group gave the Yazidis, who follow an ancient religion with links to Zoroastrianism, an ultimatum to convert to Islam, pay a tax or face death. (Ari Jala/Reuters)

When it overran the cities of Mosul and Tikrit in June, Iraqi security forces virtually collapsed, with police and soldiers abandoning arsenals of heavy weapons.

The Islamic State captured the northern towns of Sinjar and Zumar on Saturday, prompting an estimated 40,000 from the minority Yazidi sect to flee, said Jawhar Ali Begg, a spokesman for the community.

The Sunni militants have targeted minority communities in areas they have conquered.

"Their towns are now controlled by (Islamic State) and their shrine has been blown up," Begg told The Associated Press. The militant group gave the Yazidis, who follow an ancient religion with links to Zoroastrianism, an ultimatum to convert to Islam, pay a tax or face death, Begg added.

1.4 million Iraqis displaced

Iraqi Yazidi children

Iraqi Yazidi children who fled the violence in the northern Iraqi town of Sinjar. (Safin Hamed/AFP/Getty Images)

The United Nations said last month that more than 500,000 people have been displaced by the violence since June, bringing the total this year to 1.4 million, including more than 230,000 Syrian refugees. The group drove ethnic and religious minorities out of Iraq's second-largest city, Mosul, and attacked mosques and shrines claiming they contradicted strict Islamic teachings.

Kurdish forces have been battling with the militants for control of several towns stretching between the province of Nineveh and the Kurdish Iraqi province of Dahuk. At least 25 Kurdish fighters were killed in clashes with the militants on Sunday, and another 120 were wounded, according to Muhssin Mohamed, a Dahuk-based doctor.

Relations between Iraq's Kurdish autonomous region, which has its own military, and the central government, have long been strained and the announcement about the air force could indicate a degree of rapprochement in the face of the Islamic State attack.

A statement Monday by the Islamic State said it had captured dozens of Kurdish prisoners during the clashes and seized "large number" of weapons.

The authenticity of the statement could not be verified, but it was posted on a website used by the group.