Turkey and Iraq have reportedly brokered an initial agreement that could lead to allowing a Turkish role in the campaign to retake Mosul from ISIS, U.S. Defense Secretary Ash Carter said on Friday after talks with Turkish President Tayyip Erdogan.

Carter made it clear that details on Turkey’s potential role in the unfolding Mosul campaign still needed to be hammered out and a senior U.S. defense official noted non-military assistance was also a possibility.

Erdogan has previously voiced frustration that NATO member Turkey has not been more involved in the U.S.-backed assault on the Iraqi city, once part of the Ottoman Empire and still seen by Turkey as firmly within its sphere of influence.

“That will have to obviously be something that the Iraqi government will need to agree to and I think there’s agreement there in principle,” Carter told reporters travelling with him in Turkey, voicing his own conditional support for some type of Turkish role in Iraq.

“But now we’re down to the practicalities of that … and that’s what we’re working through.”

Turkey has been locked in a row with Iraq’s central government over the presence of Turkish troops at the Bashiqa camp near Mosul, where it has trained thousands of forces.

Erdogan has warned of sectarian bloodshed if the Iraqi army relies on Iran-backed Shi’ite militia fighters to retake the largely Sunni city of Mosul.