An estimated 40,000 Iraqis are stranded on a mountainside in northern Iraq without food, water or sanitation, having been forced out of their homes by IS militants.

The United Nations has received reports that 40 children have already died directly as a result of violence, displacement and dehydration, while 25,000 more minors are thought to be among those still suffering.

Those seeking safety on the mountain are members of religious minority groups from the Sinjar city area, which was taken over by the Islamic State over the weekend.

Some are Christians and Muslims, but most are Yazidis – an offshoot from Zoroastrianism which blends ancient religious traditions with both Christianity and Islam. Members of this minority faith have been targeted relentlessly by IS insurgents, who believe them to be "devil-worshippers".

Marzio Babille, UNICEF Representative in Iraq, has condemned the children's deaths as "of extreme concern" in a statement released Tuesday.

"Children are particularly vulnerable, and are most affected by the continuing violence, displacement and fighting in Iraq. UNICEF repeats its urgent call for all children in need to be protected and immediately provided with life-saving assistance to prevent further loss of life," Babille said.

"UNICEF calls all those who have influence to immediately grant children and women free and safe access to areas of refuge and respect the special protection afforded to children under international humanitarian and human rights law," he added.

Babille also underlined a concern for all those still at risk of dehydration and starvation, and warned against the threat of IS militants who are now surrounding the makeshift camps at the foot of the mountain.

Hundreds of civilians are already feared to have been murdered or abducted, and aid agencies are struggling to reach those who remain with supplies.

Amnesty International researcher Donatella Rovera has insisted that international governments must now step in.

"The plight of displaced people caught up in the fighting in Iraq is increasingly desperate and all parties to the conflict must do more to ensure their safety," she said.

"We urge the international community to provide humanitarian assistance."

Dr John Newton of Aid to the Church in Need (ACN) told Christian Today that current events in Iraq are "desperately on a bigger scale" than has ever been seen before in the country.

With thousands forced to flee their homes last night as IS militants took over four Christian-majority towns – including Qaraqosh, home to Iraq's largest Christian community – Newton says the Church is being "stretched to its limits".

"Qaraqosh was the last major Christian stronghold in Iraq, so its fall is highly significant for the future of the Christian community in the country," he explained.

"We have already seen an exodus from Qaraqosh a few weeks ago, but that was reversed shortly after when the fighting died down, but this time I think the Christians may have left for good, which means not only a humanitarian tragedy on the planes of Nineveh, but also bodes ill for the continuation of this ancient church which has been in Iraq for thousands of years.

"Other towns that fell over the weekend were home the largest and most significant Yazidi communities, so to see those towns fall also bodes ill for the presence of all religious minorities in Iraq," he added.

ACN works through local churches, and Dr Newton said they are opening their doors to people of all faiths as the escalating crisis unfolds across Iraq.

"Our partners are doing all they can to show the love of Christ to those fleeing their homes," he shared.

"Bishop Nona [Chaldean Catholic Archbishop of Mosul] has opened the doors of his church to Christians, but when Muslims have turned to him for help, he has opened up both his heart and his doors to them as well."