IRBIL, Iraq (AP) — U.S. Defense Secretary Ash Carter arrived Sunday in Irbil to get a closer look at the fight against Islamic State militants in northern Iraq and likely expand his discussions about the role of Turkish troops in the region.

Carter is expected to meet with Kurdish leader Masoud Barzani, as well as military commanders who are not far from the battle to retake the northern city of Mosul from IS.

Carter spent the day Saturday in Baghdad getting updates from his top military leadership and meeting with Iraqi Prime Minister Haider al-Abadi. He said the U.S. is prepared to provide additional support for the fight if requested by Iraq and U.S. commanders.

Iraqi Kurdish forces, known as peshmerga, have been advancing toward Mosul from the north, moving in long columns of armored vehicles. More than 100 U.S. special operations forces are embedded with the Kurds and Iraqi military commandos.

Mosul, however, is a Sunni majority town, and many worry about the involvement of government-sanctioned Shiite fighters. But they are also suspicious of the Kurds, who have ambitions to expand their self-rule area into parts of Ninevah province, where Mosul is located — although not to the city itself.

U.S. military officials say the Peshmerga will stop their military advance about 20 miles (30 kilometers) outside of Mosul and hold that territory to ensure IS insurgents don't regroup. The Shiite militias have said they will not enter the city itself.

Carter fueled debate in Iraq on Friday when he met with Turkish leaders in Ankara and suggested Turkey should play a role in the Mosul battle. Abadi on Saturday balked at that call, saying his country's own forces will oust Islamic State militants from the city.

Some 500 Turkish troops at a base north of Mosul have been training Sunni and Kurdish fighters since last December. The Iraqi government says the troops are there without permission and has called on them to withdraw. Turkey has refused, and insists it will play a role in liberating the city.

Carter and other military leaders have praised the progress of the Iraqi forces in the fight, saying the battle is proceeding according to plan.

The Islamic State group captured Mosul and the surrounding area during a lightning advance across northern Iraq in the summer of 2014.