Islamic State militants stand guard after controlling a checkpoint in Khazer at the border area of the Kurdish region yesterday.

Islamist militants surged across northern Iraq towards the capital of the Kurdish region yesterday, sending tens of thousands of Christians fleeing for their lives, in an offensive that has alarmed the Baghdad government and world powers.

Reuters photographs showed Islamic State fighters controlling a checkpoint at the border area of the Kurdish semi-autonomous region, little over 30 minutes’ drive from Arbil, a city of 1.5 million that is headquarters to the Kurdish regional government and of many businesses.

Sunni militants earlier captured Iraq’s biggest Christian town, Qaraqosh, prompting many residents to flee, fearing they would be subjected to the same demands the Sunni militants made in other captured areas – leave, convert to Islam or face death.

The Islamic State, considered more extreme than al-Qaeda, sees Iraq’s majority Shi’ites and minorities such as Christians and Yazidis, a Kurdish ethno-religious community, as infidels.

In Rome, Pope Francis appealed to world leaders to help end what the Vatican called “the humanitarian tragedy now under way” in northern Iraq. France called for an emergency meeting of the UN Security Council to “counter the terrorist threat in Iraq”.

Shares in energy companies operating in Iraqi Kurdistan plummeted on news of the sweeping Islamist advance towards oilfields in the region.

The militant group said in a statement on its Twitter account that its fighters had seized 15 towns, the strategic Mosul dam on the Tigris River and a military base, in an ongoing offensive that began at the weekend.

Kurdish officials say their forces still control the dam, Iraq’s biggest.

Yesterday, two witnesses told Reuters by telephone that Islamic State fighters had hoisted the group’s black flag over the dam.

This could possibly allow the militants to flood major cities or cut off significant water supplies and electricity.

The Sunni militants inflicted a humiliating defeat on Kurdish forces in the weekend sweep, prompting tens of thousands from the ancient Yazidi community to flee the town of Sinjar for surrounding mountains.

Some of the many thousands trapped on Sinjar mountain have been rescued in the past 24 hours, a spokesman for the UN Office for the Coordination of Humanitarian Affairs said, adding that 200,000 had fled the fighting.

“This is a tragedy of immense proportions, impacting the lives of hundreds of thousands of people,” spokesman David Swanson said by telephone.

Many of the displaced people urgently need water, food, shelter and medicine, he said. A spokesman for the UN agency for children said many of the children on the mountain were suffering from dehydration and at least 40 had died.

Christians fear they will be made to leave, convert to Islam or face death

Yazidis, seen by the Islamic State as “devil worshipers”, risk being executed by the Sunni militants seeking to establish an Islamic empire and redraw the map of the Middle East.

Thousands of Iraqis, most of the Yazidis, are streaming to the border with neighbouring Turkey to flee the fighting, Turkish officials said. In Kirkuk, a strategic oil town in the north held by Kurdish forces since government troops melted away in June, 11 people were killed by two car bombs that exploded near a Shi’ite mosque holding displaced people, security and medical sources said.

Gains by the Islamic State have raised concerns that militants across the Arab world will follow theircue. At the weekend the Sunni militants seized a border town in Lebanon, though they appear to have mostly withdrawn.

The Islamic State, which has declared a caliphate in the areas of Iraq and Syria it controls, clashed with Kurdish forces on Wednesday in the town of Makhmur, about 40 miles southwest of Arbil, the capital of the Kurdish autonomous zone.

Witnesses said the militants had seized Makhmur, but Kurdish officials told local media their forces remained in control there, and television channels broadcast footage of Kurdish peshmerga fighters driving around the town.