ISLAMIC State (Isis) fighters extended and consolidated their gains in northern Iraq today.

The militant group said that its fighters had seized 15 towns, a military base and the Mosul dam on the Tigris River.

Kurdish officials insisted that their forces were still in control, but witnesses said that Isis fighters hoisted the group’s black flag at the dam, which controls the supply of water to strategic Mosul.

Isis fighters also beat back Kurdish forces at the weekend, prompting tens of thousands from the minority Yazidi community to flee the town of Sinjar near Mosul for the surrounding mountains.

Some have been rescued in the past 24 hours, according to the UN Office for the Co-ordination of Humanitarian Affairs, but over 200,000 had fled the fighting and many thousands still remain stranded in the mountains.

A spokesman for the UN children’s agency said that many of the children on the mountain were suffering from dehydration and at least 40 had died.

“This is a tragedy of immense proportions,” said UN spokesman David Swanson.

“Many of the displaced are in immediate need of essential life-saving humanitarian items, including water, food, shelter and medicine.”

Elsewhere, Qaraqoush and at least four other predominantly Christian hamlets in Nineveh province are now in the hands of Isis fighters.

Qaraqosh, which has a population of about 50,000, lies between Mosul and Erbil, the Kurdish region’s capital in the north of the country.

Kurdish peshmerga units, which had previously protected the area, fled after clashing with Isis forces on Wednesday in the town of Makhmur near Arbil.

Isis fighters seized Makhmur and the mainly Christian town of Tilkaif, as well as al-Kwair and as many as 100,000 people are believed to be fleeing towards autonomous Kurdistan.

Across the border in Syria, Isis fighters have seized one of the last remaining government bases in the northern province of Raqqa.

Isis has controlled the provincial capital, also Raqqa, since the start of the year and has been steadily eliminating remaining government outposts in its quest to establish a religious state, or “caliphate.”