I drove into Mosul in a battered Nissan pickup truck in mid-March. Iraq’s second-largest city, once a thriving manufacturing and commercial center, is now a wreckage of destroyed factories, shops, and homes. Huge craters from bombs dropped by the U.S.-led coalition obstructed major intersections. The craters, designed to slow ISIS suicide drivers targeting the Iraqi Army, have since filled with filmy, stagnant water; they were treacherous to circumvent. Roads were lined with rubble from five months of war—chunks of concrete, twisted electricity poles and downed wires, shards of window glass. Almost every block of East Mosul was littered with charred cars. ISIS seized them from residents, setting them alight to emit black smoke and hide their movements from coalition warplanes.

There were still many bodies on the streets, even though ISIS was forced out many weeks ago. I spent an afternoon in Hay al-Tameem, or “Neighborhood of Nationalization,” a district where ISIS ran a bomb factory and confiscated homes for leaders and senior fighters. Signs in black spray paint identified houses as “Property of the Islamic State.”

“There were a lot of Russian ISIS fighters here,” Ahmed Sobhay, who lived across the street from the bomb factory, told me. Thousands flocked to the Islamic State from the Russian Republic of Chechnya, but Sobhay never dared to ask for their home towns. ISIS fighters sporadically held a gun to his head to demand his coöperation; once, they put a gun to the head of his six-year-old son, Ammer, to ask if his father was secretly smoking. Sobhay said he pulled his children out of school and didn’t let his wife or daughter go out in public for fear they would be carried off by ISIS.

“One day, one of the Russians stood at the end of the street and shouted, ‘You all have five minutes to leave,’ ” Sobhay recalled. “Then an air strike hit him—and he went straight to hell!” Sobhay chuckled.

The body of another ISIS fighter—still wearing his suicide vest—was in the front yard of the bomb factory, which, before the war, had been the home of a Mosul City Council member. The fighter’s remains had been covered with a lime-green tarp, anchored by debris to prevent it from blowing off—or the vest from blowing up. Down the street, I saw a stray boot in front of a house that had been hit by artillery. A few steps later, I saw a second boot. Walking around the wreckage that pinned the feet, I saw a blackened corpse. The fighter’s mouth was open; his teeth were still eerily white.

ISIS is estimated to have lost up to four thousand fighters since the Iraqi offensive to retake Mosul began, on October 17th. “This is the most significant urban combat to take place since World War II,” Lieutenant General Stephen Townsend, the commander of Operation Inherent Resolve, said in a teleconference from Baghdad this week. “It is tough and brutal. House-by-house, block-by block-fights,” in “claustrophobically close terrain.” More than seventeen hundred Kurdish Peshmerga died fighting the first phase of the Mosul war that opened the way for the Iraqi Army, Brigadier General Halgurd Hikmat told me. Almost eight hundred Iraqi Army troops have died in Mosul, U.S. Central Command said this week.

Civilian deaths have also soared in recent weeks, as fighting intensifies across the Tigris River in the more densely populated West Mosul. U.S. air strikes are taking a growing share of the blame, most recently on March 17th, when scores of men, women, and children were killed. Rescuers were still digging through the wreckage of several homes this week. Iraqis estimated that the final death toll may exceed two hundred, making it one of the deadliest civilian tolls since the U.S. intervened in Iraq fourteen years ago.

“If we did it, and I’d say there’s at least a fair chance that we did, it was an unintentional accident of war,” Townsend told reporters on Tuesday. “My initial impression is the enemy had a hand in this, and there’s also a fair chance that our strike had some role in it.” He said that U.S. munitions alone were unlikely to have destroyed such a large area. U.S. officials suggested that ISIS may have booby-trapped the buildings as well. An investigation, including a review of some seven hundred videotapes of coalition air strikes, is now under way.

The struggle for Mosul is unlike any other battle since ISIS seized a third of Iraq (and a third of Syria) to create its pseudo-caliphate, in 2014. In cities like Fallujah and Ramadi, the vast majority of civilians fled as the Iraqi Army fought to take back territory. In Mosul, however, the Iraqi government appealed to more than a million residents still living under Islamic State rule last fall not to leave, partly because of the challenge of caring for so many displaced people. Iraq was already struggling to accommodate some three million people displaced by the war, plus a quarter of a million refugees from neighboring countries. To cope with the strain on resources, electricity, water, and other services are now limited.

The U.S. and Iraqi strategy in Mosul has relied on precision-guided munitions to minimize collateral damage. ISIS has responded by blurring the distinction between military targets and civilian homes and businesses. Iraq claims that Islamic State fighters have forced families to gather in strategic locations, acting as human shields to ward off air strikes, the most effective tool against ISIS. Since August, 2014, the United States and eight other countries have launched more than eleven thousand air strikes in Iraq on ISIS fighters, facilities, arms depots, command and control compounds, and cash warehouses that have killed tens of thousands of ISIS forces.

By the end of the Obama Administration, there were dozens of air strikes a day in Iraq. They’ve soared since President Trump took office in January, shortly after East Mosul was liberated in a three-month campaign and the focus turned to the western sector. In his Inaugural Address, Trump vowed to wipe ISIS “off the face of the earth,” and U.S. air strikes have notably increased since then. I get a daily e-mail from U.S. Central Command detailing the numbers and locations of air strikes, which, since Sunday, have ranged between seventy and ninety-three daily attacks, against ISIS targets in both Iraq and Syria. Mosul is now hit more than any other city.

Airwars, a nonprofit group based in Britain, now estimates that more than thirteen hundred civilians have been killed in air strikes on Iraq since 2014, according to the Times. The United Nations High Commission for Human Rights called for the coalition to review its tactics “to ensure that the impact on civilians is reduced to an absolute minimum.” Human Rights Watch expressed concern about the way that the battle for Mosul is being fought since procedures to approve strikes were changed in December.

“The fact that Iraqi authorities repeatedly advised civilians to remain at home, instead of fleeing the area, indicates that coalition forces should have known that these strikes were likely to result in a significant number of civilian casualties,” Amnesty International said, in a statement, on Monday. “Disproportionate attacks and indiscriminate attacks violate international humanitarian law and can constitute war crimes.”