MOSUL, Iraq — There was a smell of death in Mosul’s Old City when Ayman Hashem came back last week to see what happened to his home. His neighborhood was unrecognizable.

“All that’s left is rubble and the bodies of families trapped underneath,” the 23-year-old said.

He flipped through photos on his phone, showing picture after picture of wreckage. His house was “cut in half,” he said. He had to cover his nose with his T-shirt because of the smell of buried, rotting bodies.

Iraq’s U.S.-backed forces wrested Mosul from the Islamic State group at the cost of enormous destruction. The nearly 9-month fight culminated with a crescendo of devastation — the blasting of the historic Old City to root out the deeply dug-in militants.

Nearly a third of the Old City — more than 5,000 buildings — was damaged or destroyed in the final three weeks of bombardment up to July 8, according to a survey by U.N. Habitat using satellite imagery.

Across the city, 10,000 buildings were damaged over the course of the war, the majority in western Mosul, the scene of the most intense artillery, airstrikes and fighting during the past five months. The survey covers only damage visible in satellite photos, meaning the real number is higher.

The population, once 3 million, is battered and exhausted, with hundreds of thousands displaced. Without a swift campaign to rebuild Mosul, aid and rights groups warn the humanitarian crisis will balloon and resentment will give way to extremism, undermining the victory.

“If the western half is ignored, it will produce a social disaster and this social disaster will create bigger destruction if it’s not addressed,” said Khatab Mohammed al-Najjar, a resident of eastern Mosul who watched the Old City burn from across the Tigris River during the operation.

“West Mosul produced Daesh, and it is very possible it may produce a new Daesh,” he said, referring to west Mosul’s historically more religious and traditional residents. He used the Arabic acronym for the Islamic State.

When Iraqi Prime Minister Haider al-Abadi declared victory in Mosul last week, he pledged reconstruction would begin soon.

But his government still struggles to finance day-to-day workings of the state amid low oil prices.

Thousands of families have been left without a home. Schools have been leveled, utility grids wrecked, highways pounded into dirt roads.

All five of the city’s bridges spanning the Tigris River have been damaged. The main hospital complex where a battle raged for more than a month is a burned out shell. Mosul’s airport looks like a derelict parking lot, booby-trapped with explosives by fleeing ISIS fighters.

In eastern Mosul, the destruction was less intense. More than 160,000 of the 176,000 people who fled the east have returned, according to the U.N. Residents have begun rebuilding homes, shops have reopened, and demining is underway.

But west of the Tigris, neighborhoods have been turned into ghost towns. There, coalition strikes killed some 5,805 civilians between Feb. 19 and June 19, according to Airwars, a London-based monitoring group tracking civilian deaths resulting from coalition actions.

Fewer than one-tenth of the more than 730,000 people who fled western Mosul have filtered back.

Saif Mohammed recently re-opened his sandwich shop on a main avenue in the west, repairing war damage with the help of a $5,000 loan from relatives. On the same street, only two or three other shops are open. His shop is a bet that residents will return.

“But what people really need is government help,” he said. “If the government doesn’t give money, there won’t be any rebuilding.”

Hiyam Mohammed hid in her home with her family on the edge of the Old City throughout the fight.

She said the only way to justice is if the government and coalition pay compensation to those who lost relatives or property.

“The government brought Daesh to us,” she said, referring to sectarian rule that fueled Sunni extremism and corruption that weakened the country’s security forces. “This mess is God’s revenge for that.”

But some in the security forces have resentments of their own, blaming residents for supporting ISIS.

“The people here have always had a rebellious nature, so they should take some responsibility for what has happened,” said Maj. Imad Hassan, a federal police officer from Baghdad. “I hope this destruction teaches them their lesson,” he said.