There are "north of 100" U.S. troops accompanying Iraqi and Kurdish peshmerga forces advancing to take back the city of Mosul from the Islamic State in Iraq and Syria (ISIS), the Pentagon said Tuesday.

It's not clear how close U.S. forces will get to the fight in Mosul, but they are allowed to embed at the lowest levels with Iraqi and Kurdish peshmerga commandos, who are expected to be carrying out the bulk of the fight.

ADVERTISEMENT

U.S. troops embedded with those forces have to stay behind the last line of concealment, the last point where they can expect contact with the enemy, said Navy Capt. Jeff Davis.

U.S. troops can also accompany the conventional Iraqi army, but at much farther distances. U.S. troops can embed at Iraqi army headquarters at the brigade and smaller battalion level, but have so far stayed at the division level.

Those U.S. forces embedded with the Iraqi army are also expected to move closer to the fight in Mosul to provide artillery support, intelligence, logistics and other support.

Davis also said U.S. Apache helicopters — which could provide close air support for Iraqi and American forces — were "ready" to be used but have not been used yet. They would expose U.S. forces to greater risk.

Davis said that so far, about 18,000 Iraqi security forces are advancing on Mosul from the south and southeast, while Kurdish peshmerga forces are advancing on the city from the east.

He also said ISIS was starting fires to obscure visibility and make it harder to hit the group with air strikes.

Davis said there was no prediction yet on how long the battle to retake Mosul will take. Mosul is the second-largest city in Iraq, with anywhere between 1 and 1.5 million civilians trapped in the city.

ISIS has held the city since sweeping across Iraq in June 2014.