BARTELLA, Iraq (Reuters) - The 9-year-old Iraqi boy was playing football on a patch of wasteground during a lull in the battle for Mosul when a mortar round fired by Islamic State militants landed nearby. It sprayed shrapnel into his lower legs and virtually severed them.

A foreign volunteer works at the emergency field hospital which is run by the US Christian charity Samaritan's Purse, eastern Mosul, Iraq March 22, 2017. Picture taken March 22, 2017. REUTERS/Suhaib Salem

Rushed by ambulance to this emergency field hospital 20 km (15 miles) east of the city, he was operated on overnight and both his feet were amputated.

He now lay sedated in a bed in a tented intensive care unit, clutching a rubber ball while Chris, a volunteer nurse from California, stroked his cheek and sang a lullaby. He probably did not yet realize he had lost his feet, she said.

There have been thousands of civilian casualties from Mosul during a five-month-long government offensive to drive Islamic State fighters from what was once their main stronghold in Iraq.

“The wounds we are seeing here are the face of war - the faces of children and mothers,” said hospital chief Paul Osteen, a surgeon from Houston in the United States. “They are beyond terror. It’s numbness.”

The flow of maimed and wounded has risen as the battle zeroes in on IS-held neighborhoods of western Mosul, where more than half a million civilians are believed to be trapped.

The militants fight with mortars, guns and car bombs, often hiding among civilians in the close-packed houses and narrow streets. The area has also been pounded by air strikes and artillery fire from Iraqi and U.S.-led coalition forces.

This mobile hospital has treated more than 1,000 patients, many of them women and children, since opening in early January.

Their wounds came from shrapnel, blasts, grenades dropped from drones and gunshots – including sniper fire that deliberately targeted civilians, staff said.

During the day, the noise of battle can be heard from Mosul in the distance, signaling that soon enough, more casualties will arrive. “We had a big run last night,” Osteen said.

One man was there after being trapped in rubble for three days. A 12—year-old boy was paralyzed from the waist down after shrapnel shredded his stomach. A 6-year-old girl with a tangled mop of hair and shining dark eyes had a hole in her leg.

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Another bed was empty. A youth had been brought in barely alive and had bled to death.

But being so close to the conflict has meant the hospital can save lives that might previously have been lost. Before it opened, the wounded often had to be taken to Erbil, an hour or two away by car depending on conditions. Some did not survive.

The mobile hospital, run by the U.S. Christian aid group Samaritan’s Purse along with Iraq’s Health Ministry and the World Health Organization, was flown in from North Carolina and erected on the Plains of Nineveh near Bartella.

Its tents and huts hold a triage room, two operating theaters, an intensive care unit with top-notch medical equipment, and recovery wards.

The doctors, nurses and other staff are volunteers, mainly but not only from the United States. Iraqi staff play a vital role, including as interpreters between doctors and patients.

During a visit by Reuters, a 12-year-old boy with a gunshot wound was stretchered in through a steel door in the concrete blast wall that surrounds the compound.

As a doctor made his assessment, an Iraqi interpreter translated his questions and soothed the frightened lad.

HATEFUL LIFE

In the recovery ward, Lazim, 32, said he had been living in an apartment that IS fighters took over. His family had survived on bread and water for the past two weeks.

During an air strike, he and his son fled. An IS mortar round landed by them and he was wounded in the stomach.

“My son’s eye popped out,” he recalled. Lazim is recovering but his son lost the eye.

Another patient, 17-year-old Omar, said he had been unable to go to school since Islamic State took over Mosul in 2014. He had once dreamed of being an oil engineer. “It was a hateful life under Daesh,” he said, using the Arabic acronym for IS.

A few days ago, he went up to the roof of their building with his father and two cousins to feed their pet birds. A mortar round hit and his right leg had to be amputated.

“Even if I get better, I don’t know what to do,” he said.

Dr. Brock Adams said they saw many serious blast wounds. “We’ve got kids with big holes in their legs,” he said. “We try not to amputate but we’ve done several in the past few days, including double amputations.”

Many of the patients were also weak and undernourished due to the lack of food, Osteen said.

Families fleeing Mosul in recent weeks have talked of high numbers of civilians killed by air strikes. The death toll is unclear but some estimates put it as high as 3,500.

Click tmsnrt.rs/2mZWV4j for graphic on Battle for Mosul