BARTELLA, Iraq — Iraqi special forces charged into the Mosul battle Thursday with a pre-dawn advance on a nearby town held by the Islamic State group, a key part of a multi-pronged assault on eastern approaches to the besieged city.

The addition of the elite troops, also known as counterterrorism forces, marked a significant intensification of the fight for Iraq’s second-largest city. As they advanced, attack helicopters fired on the militants and heavy gunfire echoed across the plains.

IS militants unleashed nine suicide car and truck bombs against the advancing troops, eight of which were destroyed before reaching their targets, while the ninth struck an armored Humvee, Lt. Col Muntadhar al-Shimmari told The Associated Press.

He did not give a casualty figure, but another officer said five soldiers were wounded. The officer spoke on condition of anonymity because he was not authorized to release information.

The special forces entered the town of Bartella, a traditionally Christian village that fell to IS in 2014, around midday. The fighting thus far has been concentrated in a cluster of towns and villages outside Mosul that are mostly uninhabited and littered with roadside bombs planted by the militants, which has slowed the Iraqi advance.

The special forces are expected to lead the way into Mosul, where they will face fierce resistance in an urban landscape where IS militants are preparing for a climactic battle. The offensive is the largest operation launched by Iraqi forces since the 2003 U.S.-led invasion, and is expected to take weeks, if not months.

The Kurdish forces known as peshmerga, who are also taking part in the offensive, announced a “large-scale operation” to the north and northeast of Mosul on Thursday.

“The operation will be in three fronts,” the peshmerga said in a statement, and follows recent gains by the Kurds to the east of Mosul and Iraqi security forces to the south.

Peshmerga forces stationed on mountains northeast of Mosul descended from their positions and charged toward the front line.