Baghdad's air force and Kurdish fighters from Syria joined forces with Iraq's embattled peshmerga Monday to push back jihadists whose latest attacks sent thousands of civilians running for their lives.

The Islamic State, or IS, raised its black flag in Sinjar on Sunday after ousting the peshmerga troops of Iraq's Kurdish government, forcing thousands of people from their homes.

The conquest of Sinjar and several other towns at the weekend threatened to further integrate the Iraqi and Syrian halves of the "caliphate" IS leader Abu Bakr al-Baghdadi proclaimed in June.

But the peshmerga declared they were mounting a counter-offensive and Iraqi Prime Minister Nuri al-Maliki on Monday ordered the air force to provide them support.

"The commander in chief of the armed forces has issued orders to the leadership of the air force and the army's aviation units to provide air support to peshmerga forces," army spokesman Qassem Atta said in a statement.

The peshmerga's fellow Kurds in Syria have meanwhile sent their own fighters across the border to help, in an unprecedented move.

"The Democratic Union Party (PYD) is fighting in the Sinjar area and Rabia," a senior army official told AFP, stressing that "it was not coordinated with the Iraqi government."

The Syria-based group posted pictures of what it said were its forces operating inside Iraq and said that PYD fighters had been battling IS militants north of Sinjar.

As Kurdish fighters converged on Sinjar, as well as the town of Zumar lost a day earlier, fleeing civilians risked being caught in the battle.

According to the UN, up to 200,000 people have fled the Sinjar area. Reports from displaced people and minority rights activists suggest smaller numbers.

The world body's top envoy in Iraq on Sunday said a "humanitarian tragedy" was unfolding.

- Homes fled in panic -

There were only patchy reports on their fate, as many ran from their homes in a panic, some embarking on a long march in the searing heat to reach the autonomous Kurdistan region, and others scurrying into the mountains.

"IS does not have that many weapons but their propaganda is very effective," said Abu Asaad, a 50-year-old Turkmen Shiite who fled to Dohuk in Kurdistan with his wife and their seven children.

"In Sinjar, they sent messages saying they would occupy the town within an hour and so everybody fled," he told AFP.

Turkmen Shiite rights activist Ali al-Bayati said hundreds of people found refuge in an abandoned factory and needed immediate assistance.

He said IS had killed the men in another group they intercepted and taken the women to an airport outside the nearby city of Tal Afar.

Many of those who fled on Sunday were Yazidis, a small community that follows a 4,000-year-old faith and has been repeatedly targeted by jihadists who call them "devil-worshippers" because of their unique beliefs and practises.

"We last had contact with them last night (Sunday) but this morning we have not been able to make contact," said Khodhr Domli, a Yazidi activist based in the city of Dohuk.

- Double threat -

"They face a double threat: nature and Daash," he said, using IS' former Arabic acronym.

The Syrian Kurds and the peshmerga have had tense relations in the past and there was no evidence the two groups were coordinating efforts to retake Sinjar.

Among the strategic gains achieved by IS over the weekend were the town of Zumar, near Mosul lake, and at least two nearby oil fields.

The "caliphate" Baghdadi proclaimed on the first day of Ramadan in late June has been attempting to create its own oil economy and securing a route from Iraq to Syria is key to their ambitions.

Several Kurdish sources said IS fighters were closing in on Mosul dam, considered Iraq's largest.

The areas conquered by the jihadists at the weekend are regions Kurdish troops moved into in the chaos that followed the IS offensive launched on June 9.

Government forces completely folded in the face of the advance and the peshmerga filled the vacuum to gain long-coveted areas they had been in dispute with Baghdad over and expand their territory by around 40 percent.

"The peshmerga are well-trained, well-equipped and motivated, but definitely more efficient fighting in defensive positions, on their own terrain, than projecting into the plains of Arab Iraq," said Peter Harling of the International Crisis Group think-tank.

Funding has also been a problem. The autonomous Kurdish regional government has not been receiving the 17 percent share of national oil revenues it is owed by Baghdad and is struggling to sell its own, smaller production independently.

In a statement boasting their latest victories, IS warned they could seek to push further into Kurdish-controlled areas.

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

The jihadist offensive in Iraq: a timeline
Baghdad (AFP) Aug 04, 2014 - Below are the main developments in Iraq, since Sunni Arab militants led by ultra-radical jihadists launched an offensive, seizing large swathes of territory in the north and the west of the country:

--JUNE, 2014--

- 10: Sunni Arab militants, led by jihadists of the Islamic State of Iraq and the Levant (ISIL), seize Iraq's second biggest city Mosul.

- 11: The insurgents seize executed dictator Saddam Hussein's hometown Tikrit, capital of Salaheddin province.

- 12: Kurdish forces take over Kirkuk to protect the northern oil hub from the militants, who have taken over several mainly Sunni Arab towns in the west of the province.

- 15: Militants take control of the Al-Adhim area in Diyala province, north of Baghdad.

- 19: The insurgents attempt to seize Iraq's biggest oil refinery outside the northern town of Baiji but after 24 hours of heavy fighting the army regains control.

- US President Barack Obama says Washington is prepared to send military advisers to study how to train and equip Iraqi forces.

- 20: Grand Ayatollah Ali al-Sistani, the highest religious authority for the Shiite majority, says the jihadists must be expelled quickly from Iraq and that the next government must avoid "past mistakes", an apparent rebuke to Nuri al-Maliki, premier since 2006 and accused of sectarian policies towards the Sunni Arab minority.

- 23: Insurgents overrun the strategic Shiite-majority northern town of Tal Afar and its airport.

- 29: ISIL declares an "Islamic caliphate" -- extending from Aleppo in northern Syria to Diyala province northeast of Baghdad. Renaming itself the Islamic State (IS), it declares its chief Abu Bakr al-Baghdadi "caliph" and "leader for Muslims everywhere".

--JULY--

- 3: Massud Barzani, the president of the autonomous Kurdish region asks its parliament to start organising a referendum on independence.

- 5: Baghdadi, appearing for the first time in a video released on social media, orders all Muslims to obey him.

- 9: Maliki accuses the autonomous Kurdish region of harbouring jihadists. The Kurdish authorities say Maliki has "become hysterical" and should step down.

- 15: In a rare sign of success, tribesmen and security forces succeed in driving out militants from Dhuluiyah, 80 kilometres (50 miles) north of Baghdad after days of heavy clashes.

- 18: Christians flee Mosul after mosques relay an ultimatum giving the minority a few hours to leave.

--AUGUST--

- 2-3: The IS conquers several Kurdish-held towns, including Sinjar and Zumar near the Syrian border, ousting Kurdish peshmerga fighters.

- 4: Maliki orders the airforce to provide support to peshmerga forces in their battle against jihadists.