WASHINGTON – The Defense Department said Tuesday that no U.S. troops will go to the front lines in the battle of Mosul which launched Monday. But the U.S. is playing a key advisor role in helping Kurds and Iraqis on the battleground.

Approximately 10,000 Kurdish Peshmerga and 18,000 Iraqi security forces (ISF) are fighting in Mosul, and the numbers could go up, said Pentagon spokesmen Army Capt. Jeff Davis to a group of reporters. With them are over 100 U.S. troops, providing advice and assistance.

In June 2014, ISIS stunned the West by seizing Mosul, Iraq’s second-largest city. It is the biggest city under ISIS control and its last remaining stronghold in the country, a key part of the so-called Islamic State’s legitimacy. Since 2014, Iraqi government offenses have been trying to reverse ISIL’s territorial gains in Fallujah, Ramadi, and elsewhere.

On Monday, several villages east of Mosul were liberated in historically Kurdish areas by the Peshmerga in a sort of “leapfrog effect” strategy. Kurdish fighters advanced first in historically Kurdish villages, and the Iraqi forces followed right behind them.

As the combined advance toward Mosul, Davis predicts that the Iraqi units will primarily take the lead.

“The level of coordination and cooperation that we have seen between the Kurds and the ISF has been very good,” Davis said Tuesday. “They are working together very well, collaborating just the way we would want them to.”

On the other side, obscuration fires – giant pits filled with oil and tires lit to create thick, black clouds of smoke – and suicide bombers continue to be strategies for ISIS.

As the fighting intensifies, it’s the civilians who will suffer the most. The Pentagon said that the ISIL is using civilians as human shields in Mosul, a tactic that’s not new.

“We’ve seen civilians being forcibly detained and their movements being prevented where they can’t get out of Mosul. They’re being held there against their will,” Capt. Davis said.

The United Nations estimates that 1.5 million people live in the Mosul area. Shelter is available for 60,000 people in camps and emergency sites; food rations for 220,000 families are ready for distribution, according to a statement on Sunday by Stephen O’Brien, the UN’s under-secretary general for humanitarian affairs and emergency relief.

But more humanitarian efforts will be needed, since it’s unclear how long the offensive will take. “It’s Day 1, don’t get your hopes up, it’s going to be a while. But it is very much underway,” Davis said.