Thousands of families are living in a “smoke-filled hell” in Iraq after Isis militants set oil wells ablaze as they retreated from towns and villages as Iraqi forces advance towards Mosul.

An aid worker on the ground has told The Independent children’s faces are “black with soot” and people are developing severe breathing problems as jihadis intentionally set fire to wellheads in areas they are being pushed out of - reportedly as a way of both protecting themselves from air assaults and further "terrorising" local people.

Several thousand people are currently said to be affected by the fires, which emit smoke that travels up to 20 kilometres.

In the town of Qayarrah, located 30 kilometres south of Mosul, more than 60 homes were completely destroyed at the end of August when jihadis reportedly rigged wellheads with improvised explosive devices (IED) before using snipers to shoot at them until they exploded, throwing oil out to the surrounding areas.

The raging fires that followed are still ablaze two months on and The Independent has heard how residents suffering the consequences of living in a blanket of smoke.

An Oxfam spokeswoman who has been working regularly in Qayarrah since August, said the smoke is now many people's "number one concern" as children's health deteriorates.

On some days in Qayyarah the air is so thick with black smoke that it completely blocks out the sun (Sam Cunningham/Oxfam)

She stold The Independent: “The children’s faces are black with soot. They are coughing and wheezing. Many have developed rashes on their body from being constantly covered in the substance, which is extremely difficult to remove.

“This is now people’s number one concern in a lot of these areas. It’s difficult to breath, they’re having chest problems. A doctor told me patients are having bronchitis type symptoms – wheezing, coughing and struggling to breath.

"Isis are doing this as a way to cover themselves from air assaults – with the thick smoke that blocks the sun – as well as to further terrorise local people before they retreat from towns and villages.

“People are already traumatised. Speaking to people it’s heartbreaking because they lived under Isis control for about two years in these places – some longer – and you can only imagine the kind of lives they had under Isis control, especially women.

“They’ve been terrorised and they’ve had a real lack of access to services, water, food and jobs. Then they've had to deal with the fighting that ensued when these places were captured. And now they’re having to deal with the smoke and its health effects.”

Dr Majda Abdelaziz (whose name has been changed), a doctor in a cluster of villages just outside Qayarrah, said children were suffering from scabies and bronchitis as a result of the fires and that there was a severe shortage of medication to treat them.

Isis rigged 15 oil well heads with explosives and set them off by shooting at them from nearby buildings, causing wells to explode and sending gallons of oil into the air, landing in families' homes (Amy Christian/Oxfam)

Dr Abdelaziz said: “There’s been no fuel here for two days now. Children here are suffering from scabies and bronchitis, which is caused by the air pollution from the burning oil fields and sulphur plant.

“We have roughly twenty children of different ages coming to the clinic every day with these issues. They need steroid cream for their skin but we have a shortage of medicine. I arrived here eight days ago and there were no drugs.

“Drinking polluted water is also causing the gastritis. The sulphur is making things much worse. Not just for the children but for the adults too.”

The concern is heightened by the fact that Qayarrah and surrounding areas are expected to see an influx of more people in the coming weeks, with thousands of Iraqis likely to flee to from villages and towns closer to Mosul as jihadi forces retreat further towards the city and continue to set wellheads ablaze.

The Oxfam spokesperson expressed fears the substance would pollute the drinking water in affected areas, with the added fear that thousands of people living further north will soon arrive. “There are concerns that the soot and the pollution in the air will transfer into the main water source, causing further health complications for people," she said.

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“In the next few weeks we imagine there’s going to be a large number of people fleeing to that area and they are also going to have to deal with the air pollution and its effects."

Oxfam is calling on the Iraqi government to prioritise extinguishing the fires and to seek external support if necessary, and to explain to communities what is being done and when they can expect this to happen.

Andres Gonzalez, Oxfam’s country director in Iraq, said: “Even after Isis has left, many of the people living amid its trail of destruction have told us that life remains unbearable.