MOSUL, Iraq — As Iraqi forces pushed into southwestern Mosul, four Islamic State fighters moved into Omar Khudair's home and took up positions on the roof.
The 17-year-old, his parents and siblings took cover in his aunt's house next door, and for the next half hour they huddled in a back room as the battle raged overhead. Then the airstrikes came, blowing up a cluster of houses, killing not only the fighters, but 18 members of Khudair's extended family. The teen was one of the few to survive, left covered in burns and shrapnel wounds.
The fight for the western half of Mosul could the deadliest yet for civilians. Iraqi forces have increasingly turned to airstrikes and artillery to clear heavily populated, dense urban terrain, and residents running out of food and supplies are fleeing their homes at higher rates than previously seen in the Mosul operation.
More than 750 civilians have been killed or wounded since the fight for western Mosul began a month ago, front-line medics say, a number they expect to spike as Iraqi forces push into the old city. They spoke on condition of anonymity in line with regulations.
By comparison, some 1,600 civilians were killed or wounded during the 100 days of fighting to recapture Mosul's less densely populated east, according to reports from nearby hospitals. Mosul's east was declared fully liberated in January.
Airwars, a London-based group that tracks civilian deaths from airstrikes targeting IS in Iraq and Syria, estimates the number of casualties to be much higher, claiming more than 300 civilians have been killed in western Mosul over the last month.
The Pentagon, which has yet to release casualty figures from the last month, has acknowledged 220 civilian deaths from coalition airstrikes in Iraq and Syria since the U.S. campaign against IS began in 2014.
Of the nearly 300,000 people who have fled Mosul since the operation to retake Iraq's second largest city began in October, more than 100,000 have left in the past month alone, according to the United Nations.
Many are fleeing because they have no more food, said Azher Adnan, a local pharmacist volunteering as a medic at a clinic just south of the city. "Every one of my patients, the first thing they say when they approach my clinic is 'I'm hungry,'" he said.
Civilians who have escaped said food began to run low in October as the wealthy hoarded what they could. By January, grocery store shelves were completely bare.
"The population of Mosul's west is different from the east," Adnan said. "Here you have more people in poverty, they couldn't afford to prepare for the siege."
In eastern Mosul, most militants withdrew in the face of the assault, leaving small contingents of four of five fighters to pin down troops in urban combat. But Lt. Gen. Sami al-Arathi, of Iraq's special forces, said the fighters cornered in west Mosul have nowhere to run. "Now, they are forced to fight to the death," he said.
Faced with heavier resistance in more dense urban terrain, Iraqi forces are relying even more on airstrikes and artillery, heightening the risk to civilians and leaving scenes of devastation in their wake.
"This area used to be so beautiful," said Mohammed Ali of the Federal Police, which have been battling their way up the Tigris along what used to be a scenic riverside boulevard, leaving behind mangled park benches and shattered flower boxes.
Ali, who hails from a town just outside Mosul, remembers spending time on the corniche as a teenager.
"Families and girls would come here," he said, laughing. "We used to follow the girls, but they never gave us any attention."
U.S. Army Maj. Gen. Joseph Martin, the commander of coalition ground forces in Iraq, said the coalition is "probably" launching more airstrikes in western Mosul than in the east because more coalition troops have been authorized to approve air support for Iraqi forces.
"We're going to strike ISIS wherever we can so that the Iraqis can be successful," Martin said, referring to the extremist group by another acronym.
He said changes to the U.S. rules of engagement are allowing the coalition to strike faster and more accurately. Martin said Iraqi commanders are still trying to preserve infrastructure and minimize civilian casualties — but that the militants have other ideas.
IS has fired at least 4,284 mortars, rockets, and artillery rounds "indiscriminately" in western Mosul since January, showing "complete disregard of human life," he said.
Humanitarian organizations warn that the destruction, displacement and civilian casualties are likely to spike as Iraqi forces push into Mosul's old city, where streets are the width of alleyways.
A senior Western diplomat who attends military planning meetings said Iraq's military showed that they were capable of protecting civilians in eastern Mosul, but will face a much greater challenge in the old city.
"In the old city (Iraqi forces) are going to have to get out of their vehicles and they've got to go house to house," the official said on condition of anonymity to discuss military planning. "Families are going to be at extreme risk."
In Mamun, one of the first western Mosul neighborhoods to be retaken from IS, nearly every customer at a corner vegetable market knew at least one person who had been killed during the past month's fighting.
Ahmed Khalil pointed to where he said a rocket had killed a mother and her children. He gestured further down the street, where he said IS snipers had picked off civilians trying to flee.
"We couldn't even take the bodies to the cemetery because the clashes were so heavy," he said. "We had to just bury them where they fell."
Another customer, Mashad Fathi, pointed to a street where a whole row of buildings had collapsed. "The bodies of one of the families are still under the rubble."