Jihadists from the Islamic State (IS) group captured the city of Qaraqosh in Iraq last night, forcing thousands to flee.

Militants pushed back Kurdish troops and then moved in overnight to take over four Christian-majority towns, including Qaraqosh which is home to Iraq's largest Christian community.

"I now know that the towns of Qaraqosh, Tal Kayf, Bartella and Karamlesh have been emptied of their original population and are now under the control of the militants," Chaldean archbishop of Kirkuk and Sulaimaniyah, Joseph Thomas, confirmed to AFP.

"It's a catastrophe, a tragic situation. We call on the UN Security Council to immediately intervene," he urged.

"Tens of thousands of terrified people are being displaced as we speak, it cannot be described."

A Tal Kayf resident who witnessed the events last night told AFP that the city is "now in the hands of the Islamic State".

"They faced no resistance and rolled in just after midnight. I heard some gunshots last night and when I looked outside, I saw a military convoy from the Islamic State. They were shouting 'Allahu Akbar' (God is greatest)," Boutros Sargon recalled. He has been forced to join the thousands who are fleeing the escalating violence.

Qaraqosh and the surrounding towns are said to have contained at least a quarter of Iraq's historic Christian population before the insurgents moved in.

This latest move from IS comes amid increasing violence and persecution in Iraq, as militants – who follow a fundamentalist strain of Sunni Islam – attempt to form a caliphate across a stretch of Syria and Iraq.

In 2003, there were around 1.5 million Christians living in Iraq. There are now thought to be less than 200,000.