The Islamic State has launched 632 vehicle bombs against Iraqi forces since their offensive to reclaim the city of Mosul began six weeks ago, a senior military official said Thursday.

The widespread use of vehicle-borne bombs — at a pace that amounts to 14 per day — has helped make the battle for the militants’ largest stronghold in Iraq particularly treacherous. ­Local troops are taking significant losses as they face a well-armed adversary in close-range firefights, while civilians bear the brunt of relentless militant shelling.

The stakes are high for the Iraqi government and its U.S. backers as they orchestrate a massive, multipronged attack on a large, densely populated city that has been under extremist control for 2½ years.

In his first televised update since the offensive began, Lt. Gen. Abdul Amir Yarullah, who commands the ongoing operation, said Iraqi fighters had made significant progress in clearing the Islamic State from villages surrounding Mosul and, in recent weeks, had captured a growing number of neighborhoods within the militant-held city. The United States and its allies are also conducting airstrikes in support of ground forces.

Yarullah described some of the challenges that an array of Iraqi fighters — including army, federal police and elite counterterrorism troops, along with local tribesmen and Iranian-backed militiamen — had encountered. Explosive-mounted vehicles — including cars, trucks, armored personnel carriers and even armored bulldozers — have been a hallmark of the militants’ effort to hold off advancing forces.

[The mounting death toll in Mosul forces questions about the battle plan]

While Iraqi troops have disabled many of the bombs before militants could set them off, some of the vehicles have struck their targets with deadly results. An Islamic State video released last month showcased a variety of such attacks, some of which set off massive explosions and sent Iraqi forces fleeing for their lives.

While insurgent car bombs are nothing new, countering those attacks has become much more difficult within the narrow streets and tightly packed homes of ­Mosul. The thick armor that militants apply to the vehicles make them harder to disable, while the density of the populated urban area means airstrikes are more risky.

While Iraqi officials have said the pace of car bombs has dropped off as the battle wears on, militants retain substantial firepower.

The general provided his update on the 45th day of an operation that has proved deadly for civilians, tens of thousands of whom have already fled the city. Those who remain risk being caught in the crossfire or being struck by mortar shells that militants are firing at recently recaptured neighborhoods. According to a U.N. report released Thursday, nearly 900 civilians have died in Nineveh province, where Mosul is located, since the beginning of October.

Yarullah said the presence of more than a million civilians was a central factor in the pace of advance, which has slowed as troops try to press further into the city east of the Tigris River. “If it wasn’t for the civilians and the need to protect them, [our troops] would have gone much more quickly,” he said.

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Iraq has never seen this kind of fighting in its battles with the Islamic State

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