IRBIL, Iraq — Iraqi forces opened a new front Thursday in their offensive to retake Mosul, advancing from the northwest in a bid to add momentum to the grueling seven-month-long battle for the city.

Troops from the army’s 9th Division and elite forces from the Interior Ministry spearheaded the early morning attack, according to the Iraqi military.

Islamic State militants are still holding on in a few neighborhoods of western Mosul, after losing control of the east. But the Iraqi offensive, which is backed by airstrikes and military support from a U.S.-led coalition, had slowed in recent weeks. Interior Ministry forces have ground to a halt on the southern edge of Mosul’s Old City, whose narrow streets and winding alleys are inaccessible to armored vehicles.

Given that challenging geography, Iraqi commanders have said they now plan to lay siege to the Old City by attacking from the northwest. But the district remains home to hundreds of thousands of civilians, raising concerns for their welfare as the battle closes in, and food and drinking water become increasingly scarce.

“The Old City will be isolated and the last target,” said Lt. Gen. Sami al-Aridhi, a counterterrorism forces commander. He said authorities are considering dropping humanitarian aid to families trapped in areas held by the Islamic State.

Nearly half a million people have been displaced since the battle for Mosul began in October, according to the United Nations. Some have fled to relatives in the city’s east, which is now under the control of Iraqi security forces.

Others have had no choice but to stay in poorly supplied camps south of the city. Aid groups say they expect a new flow of displaced families as Iraqi forces push from the north.