At least two people have been killed and hundreds more exposed to choking fumes after ISIS torched up to 19 oil wells and a sulphur plant near Mosul in Iraq.
The militants began lighting the infernos in August, possibly to mask their movements as US-backed Iraqi forces launched an offensive to regain control of the city.
NASA images taken on 22 October show two enormous plumes rising from the area, dark brown smoke from the Qayyarah oil field and clouds of white sulphur dioxide from the Al-Mishraq sulphur plant.
The sulphur blaze was extinguished on 23 October, but the toxic fumes killed two people and 1000 others have reportedly sought treatment for breathing problems.
Meanwhile, the ferocity of the oil fires has hampered the efforts of local fire crews to extinguish them amid fears that explosive devices may have been planted around the wells.
Local people say the smoke is burning their throats and lungs, blocking out the sun and coating their skin in black, oily soot. Civilians are also suffering from headaches, skin rashes and chest pains, according to Oxfam.
When crude oil is burned, a large number of toxic chemicals are released, including carbon monoxide, lead, polycyclic aromatic hydrocarbons and volatile organic compounds, says
Bin Jalaludin at the University of New South Wales in Australia. These can harm the passages of the nose, airways and lungs, making it difficult to breathe.
There is now the danger that ISIS will set alight the other six oil fields that it controls near Mosul, says Oxfam.