Jihadists seized much of Iraq's Christian heartland and moved within striking distance of autonomous Kurdistan on Thursday in a push that stirred panic among residents and alarm in Western capitals.

Amid reports Washington was pondering air strikes, the UN Security Council prepared for emergency talks following a sequence of attacks that saw Islamic State (IS) militants extend their writ over northern Iraq in less than a week.

Jihadist fighters moved into Qaraqosh, Iraq's largest Christian town, and surrounding areas on Wednesday night after the withdrawal of Kurdish peshmerga troops, who are stretched thin across several fronts.

"Qaraqosh, Tal Kayf, Bartella and Karamlesh have been emptied of their original population and are now under the control of the militants," Joseph Thomas, a Chaldean Catholic archbishop in northern Iraq, told AFP.

Tal Kayf, the home of a significant Christian community as well as members of the Shabak Shiite minority, also emptied overnight.

"I heard some gunshots last night and, when I looked outside, I saw a military convoy from the Islamic State... shouting 'Allahu Akbar' (God is greatest)," said Boutros Sargon, a resident who fled and was reached by phone in Arbil, capital of Iraqi Kurdistan.

Chaldean Patriarch Louis Sako, who heads Iraq's largest Christian denomination, said the overnight offensive had displaced 100,000 Christians.

"This is a humanitarian disaster. The churches are occupied, their crosses were taken down," he told AFP, adding that 1,500 manuscripts had been burnt.

Last month, IS militants forced Christians out of the main northern city of Mosul they conquered at the very beginning of their offensive two months ago by demanding they convert to Islam, pay protection money or leave on pain of death.

- US decision -

With Kurdish and Iraqi federal troops proving unable to stop the rot, calls have mounted for international intervention against the jihadists before they can consolidate a "caliphate" straddling Iraq and Syria they proclaimed in June.

US President Barack Obama, who ended his country's eight-year occupation of Iraq in 2011, was expected to "imminently" decide on possible airstrikes.

The Security Council meeting -- due to start at 2130 GMT -- was requested by France, whose President Francois Hollande said he was ready to "support forces" battling the jihadists.

He spoke after a conversation with the leader of Iraq's Kurdish region, Massud Barzani, but did not specify what kind of support France was offering.

The latest IS advance means jihadists are now in some areas barely 20 kilometres (12 miles) from the official border of the Kurdish region and 40 kilometres from Arbil.

The group launched a devastating offensive on June 9, seizing the country's second city Mosul the next day and sweeping across much of the Sunni heartland.

Peshmerga forces apparently redeployed to Arbil some of the forces they had assigned to the disputed land they grabbed from the government during the army's initial debacle.

They also beefed up security in Kirkuk, the most significant conquest they made during the June chaos, but the city was rocked by a car bomb Thursday.

The blast ripped through a Shiite mosque where displaced people had sought refuge, killing at least nine, police and medical sources said.

- Mountain death trap -

The experienced peshmerga were thought to be a sufficient bulwark against massive further advances by the jihadists, but IS fighters have been moving stealthily across the northern Nineveh province and making surprise gains.

At the weekend, IS units took over most of the Mosul hinterland which the peshmerga had occupied after government forces retreated in June.

Among its conquests was the Sinjar area, from which tens of thousands of civilians fled, including many families from the Yazidi minority who are still hiding in nearby mountains.

The Yazidis, and other local residents, have been stranded in the mountains since Saturday with little food and water.

Fares Sinjari Abu Ivan, a Yazidi beekeeper who fled with his 80-year-old mother to the barren mountains, told AFP by phone that some groups had attempted to flee but with mixed results.

"We have spoken to some who made it to Turkey but in their flight, they encountered Daash (Islamic State) fighters who cut the road. Some fled, some were killed and others came back to the mountain."

The leaders of the small minority, who practice a 4,000-year-old faith rooted in Zoroastrianism, have warned that their entire community risks being massacred or starved into extinction.

Turkish officials said up to 800 displaced Sinjaris had made their own way to Turkey, while the Turkish Kurdish group PKK said it had evacuated several families after opening a safe passage to Syria.

IS, meanwhile, boasted of its latest victories.

"We are pleased to announce to the Islamic nation a new liberation in Nineveh province, teaching the secular Kurds a lesson," it said.