AL QAYYARAH (Iraq) • Clad in red helmets and surgical masks, the firefighters emerged exhausted from the massive column of smoke streaming almost incessantly out of an oil well in northern Iraq.

They had been struggling for hours to pump water into the well near Qayyarah, a small town in the Iraqi desert 60km south of Mosul.

Along with oil engineers and police officers, firefighters have been working non-stop to extinguish more than a dozen wells lit by militants of the Islamic State in Iraq and Syria (ISIS) in August to slow government forces advancing on Qayyarah as part of their drive to wrest back Mosul from the clutches of the extremists.

The wells have been belching columns of toxic black smoke for more than three months, caking everything in and around Qayyarah in a thick layer of soot.

On Sunday, the firefighters' silhouettes were barely visible as they stood over the burning well near Qayyarah, where the mid-afternoon sun was dimmed by the black clouds overhead.

Trucks filled an adjacent reservoir with water, which was then pumped through a pipeline manually assembled by workers at the site into each well.

Putting out the fires has proved to be a complex and dangerous process. "First, the federal police have to check for mines left by ISIS at the mouth of the oil wells," said Mr Saleh Khodr Ahmad, a worker at the site. Once the area is cleared and the blaze brought under relative control, firefighters "place a pipe into the mouth of the well to pump water in, and cover it with dirt", he said.

The whole process can take up to a month and only two of the 19 lit oil wells have been extinguished.

"I'm exhausted; my body has been destroyed," Mr Ahmad said.

According to the UN's environmental programme, crude oil fires "produce a wide range of pollutants, including soot and gases that cause health problems such as skin irritation and shortness of breath".

A pair of firetrucks and ambulances were parked at the ready in the sand nearby.

"The ambulances are here to treat the cases of suffocation and any injuries from explosives," said police officer Ismail Ali Mohammed, who is guarding the site.

One of his colleagues was killed last Saturday after he stepped on a mine at the same well that firefighters are trying to bring under control.

"I've been here for 15 days, working 24-hour shifts. We've all been poisoned by this smoke," said Mr Mohammed, whose family still lives in an ISIS-controlled part of Mosul. "This is a terrible scene, a deplorable situation."

AGENCE FRANCE-PRESSE