MOSUL, Iraq — The operation to liberate the Iraqi city of Mosul is the most intense urban combat anywhere in the world in recent times, Maj. Gen. Joseph Martin, head of ground forces for the U.S.-led coalition fighting Islamic State, said Wednesday.

Five thousand civilians and 1,600 Iraqi troops have been killed and injured in Mosul since the operation to retake the city began in mid-October, according to Iraqi officials.

Islamic State fighters, who occupied Mosul more than two years ago, have had ample time to turn it into a deadly urban battlefield. Besides intricately prepared defensive positions and tunnel networks, advancing Iraqi forces have had to contend with hundreds of armored cars and trucks bearing improvised explosive devices. These usually emerge suddenly from nearby garages and other concealed locations, leaving little time for troops to react with airstrikes or shoulder-launched rockets.

Such tactics have significantly slowed the Iraqi advance and drawn unfavorable comparisons to the recently ended campaign in neighboring Syria, where government forces and their allies drove out entrenched rebels from Aleppo after just five weeks of intense combat.

“Some of the hardest door-to-door fighting the world has seen in many years,” Martin, who commands the 1st Infantry Division, said on his “Danger 6” Twitter account about the situation in Mosul.

On Wednesday, heavy gunfire and explosions rocked Mosul’s al-Arabi neighborhood, which runs along the east bank of the Tigris River.

Burned-out cars, unexploded munitions and the bodies of Islamic State fighters lay in the street.

Despite the risks, some residents were heading home.

Wrecked vehicles and earth fortifications meant the only way into al-Arabi was on foot, though some people carried bicycles over the obstacles.

Nasar Mohamad Ali, his wife and four children, clambered through bomb craters, avoiding streets where bullets still flew, as they dragged suitcases toward their house.

“Daesh were retreating across the river, and they told us to come with them,” Ali said of their escape last Friday, using a the Arabic acronym for the Islamic State group.

Instead, the family fled across the battlefield to government-held areas while the militants were harassing their neighbors, he said.

The civilians passed a dead enemy fighter in a camouflage uniform. What appeared to be a suicide belt lay a few feet from the body. A man pushing a woman in a wheelchair spat on the corpse. Then a teenage girl laughed and gave it a kick.

Huseen Tallal Saleh stayed in his home during the battle for the suburb.

The first Iraqi special forces troops to reach the area ordered residents to block the streets with their cars, he said.

However, Islamic State fighters returned and forced people to burn their own vehicles. “If we didn’t do it, they said they would kill us,” Saleh said, standing beside the blackened wreck of his car, one of many blocking the road.

Another al-Arabi resident, Amar Hani Sheet, said Shiite militia arrived soon after the special forces troops and defiled the bodies of Islamic State fighters.

Iraqi troops hunkered down nearby said they expected an even tougher fight when they push across the river into the western part of the city. There the enemy is dug in among an estimated 750,000 civilians in some of Mosul’s oldest neighborhoods and winding streets too narrow for armored vehicles.

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