An Iraqi special forces soldier puts up a helmet as a decoy as a sniper prepares to fire on Islamic State positions on the eastern edges of Mosul on Thursday. (Marko Drobnjakovic/AP)

The vehicles screeched into the small field hospital on the outskirts of Mosul carrying desperate loads: soldiers injured in battle as well as men, women and children caught in the crossfire of Iraq’s war against the Islamic State.

Some staggered out clutching bleeding wounds; others were lifted by medics onto stretchers. They had come face-to-face with chlorine gas, mortar fire, bombs and artillery shells.

For a few, it was too late, and instead of a stretcher, a body bag waited.

The medical station, manned by medics from Iraq’s special forces alongside U.S. and Slovak volunteers, provides a small window onto the inevitable human toll of the battle to oust the Islamic State from Mosul as the war pushes deeper into the city.

After more than two weeks of advances, Iraqi forces are now pressing into more densely populated areas and penetrating the epicenter of the group’s last remaining territory in the country.

The civilian presence hugely complicates the fight for the advancing Iraqi forces and airstrikes from the U.S.-led coalition, a fact the Islamic State is using for its gain as it desperately tries to hold onto its capital in Iraq. (Loveday Morris/The Washington Post)

As they do, Iraqi commanders say Islamic State militants are putting up a tougher fight than they have ever seen, bringing furious battles to the doorsteps of more than a million people.

The civilian presence hugely complicates the fight for the advancing Iraqi forces and for airstrikes from the U.S.-led coalition, a fact the Islamic State is using for its gain as it desperately tries to hold on to its capital in Iraq.

For more than a year, the militants have largely prevented people from leaving the city, but in recent weeks they have rounded up villagers from the outskirts and forced them inside the city to use as human shields.

“Head injury!” shouted Maj. Ahmed Hussein, the medical station’s chief medic, as a 16-year-old girl arrived in a family sedan. After laying her on a stretcher, medics bound her head, trying to stanch the flow of blood from a shrapnel wound. “May God take revenge on Daesh,” cried her mother, using a derogatory term for the Islamic State.

Before the team had finished treating her, another casualty arrived: a tank driver struggling to breathe after a suspected chlorine attack. He was drained of color, and his chest trembled as he tried to fill his lungs. The militants have regularly used chlorine on the battlefield, often dispatching it in mortar shells.

“That’s our sixth or seventh chlorine gas,” said Derek Coleman, 27, from San Diego, who came to Iraq with hopes of fighting the Islamic State but said he later realized he could be of more use as a medic.

Coleman, two other Americans and two Slovaks were spending their first day with Iraqi forces after previously assisting Kurdish peshmerga soldiers.

The Iraqis do not appear to have much need for them, he said, as the Iraqi special forces have better-organized medical teams. But Hussein said he still appreciates the extra hands and supplies.

Hussein said more civilians have been injured in recent days, although he was quick to point out that the Islamic State is responsible. “They use civilians as a shield,” he said.

Over the course of the day, Hussein’s station treated 15 civilians, one of whom died from gunshot wounds. Many, though, are probably unable to reach medical assistance, and those fleeing talk of entire families killed in shelling and bombing.

But the militants do not appear ready to concede ground easily, potentially drawing out the fight and putting civilians at risk for longer.

The Iraqi military does not release overall casualty figures, but troops have faced stiff resistance as they have broken into the Islamic State’s last major urban stronghold in Iraq.

Some 11 special forces troops were treated for injuries at the medical station, while two died. Not all Iraqi casualties pass through this point, and the toll is probably much higher. News of new car bombs crackled through on the radio.

“They are fighting very, very hard for the city,” said Lt. Gen. Abdul Ghani al-Asadi, head of the special forces, also known as counterterrorism troops. “They will not give it up easily.”

Friday’s fight in urban areas was extremely tough, he said, adding that the taking of people to use as human shields “has complicated the battle in a way we didn’t expect.”

A black Humvee pulled up at the medical station, which is little more than a few beds and stretchers near an abandoned mosque in Gogjali district, on the eastern edge of Mosul.

Men cried out for a body bag. The body of a soldier from Iraq’s special forces was lifted out of the back. The top of his head, from the jaw up, was missing. His clothes were soaked in blood.

“This is war,” Hussein said as he turned away.

The Iraqi government is trying to keep people in their homes during the fighting, but as the battle draws near, many inevitably flee.

The sound of heavy bombing and gunfire could be heard coming from the city, while Apache helicopters flew back and forth. Cars topped with white flags continued to stream out of eastern neighborhoods.

For those who stay, even after their areas are cleared of militants, food supplies are low, forcing many out. A woman from Gogjali arrived at the medical station with her young daughter, who held a white flag fashioned out of a small piece of cloth attached to the end of a kitchen whisk.

The woman, who was too scared to be named, asked the soldiers to break open a shop that she said used to belong to the Islamic State and had sold milk before it had been locked up when the militants fled.

“I’ll put money in the register. I just need milk for my baby,” she said.

Hussein said that he could not break into private property and that it might be booby-trapped, but he dispatched a soldier to find milk.

Another car pulled up at the makeshift clinic carrying two injured children. One had a bone jutting out of his mangled arm. His chest was gouged by shrapnel. He had been playing near his house when he picked up something that looked like a grenade.

“I told him to leave it,” said Ayman Ouda, the boy’s elder, 11-year-old cousin, who was lightly injured. “But he dropped it, and it exploded.”

Medics surrounded the younger boy, and Hussein called for a drip. His fracture was treated, and he was rushed into the back of a waiting ambulance. But Peter Reed, 27, from Bordentown, N.J., and another volunteer here, is not hopeful.

“He’s probably not going to make it to the next med station,” he said.

Correction: An earlier version of this article incorrectly described some of the volunteers helping medics in northern Iraq as Serbian. They were from Slovakia.