The plan to cut off the city of Raqqa, the capital of the self-proclaimed Islamic State, could begin as early as “two weeks,” a U.S. defense official told The Daily Beast Thursday.

But which troops would eventually enter Raqqa after it is surrounded—and how the U.S.-led coalition would choose which warring allies should be involved in the invasion of Raqqa—have yet to be sorted out. In other words: U.S. military this week may have begun to trumpet the definitive battle to defeat ISIS, but they have yet to finalize the details of how the battle for Raqqa would shake out, defense officials conceded to The Daily Beast.

Instead, there are dueling battle plans emerging between purported NATO partners. The U.S.-led coalition is saying that the fight for Raqqa is about to begin, led by Kurdish forces known as the YPG. Turkey, meanwhile, is vowing to stop the YPG.

The U.S. military has said it believes the best way to defeat ISIS is to launch simultaneous operations against two major cities under the terror group’s control, Raqqa and Mosul, which serve as capitals of its self-declared caliphates in Syria and Iraq, respectively. The Iraqis launched the campaign to liberate Mosul 10 days ago.

But there’s no equivalent to a friendly Iraqi army in Syria. Instead, the U.S. military’s most effective local ground force against ISIS has been the YPG. Two defense officials told The Daily Beast that the YPG would only be a part of what the U.S. military calls the move to “isolate” Raqqa, building essentially a ring around the city to stop ISIS movement in and out.

The defense officials said the YPG would not enter the city, a concession to Turkey which considers the YPG a terrorist group.

The YPG are part of the so-called Syrian Democratic Forces, which also include Arab fighters. And the U.S. said it plans for Arab members of the SDF, in addition to yet to be trained additional Arab forces, to actually enter Raqqa. According to BuzzFeed, Turkey this month began training some of those Arab fighters for the battle for Raqqa, with U.S. backing.

The battle for Raqqa is driving a wedge between the United States and its NATO ally, Turkey, even as they say they both want to see the demise of ISIS in Syria. On Thursday, the defense officials said there are ongoing discussions with Turkey about the operation to liberate Raqqa.

Tension between Turkey and United States has only increased in the last two days, since the U.S. declared its commitment to working with the YPG forces, over Turkish objections. On Thursday, Turkish President Recep Tayyip Erdoğan announced in a speech in Ankara that Turkish troops would rid the northern Syrian city of Manbij, which Kurdish forces help capture from ISIS in August, of Kurdish forces, and eventually do the same in Raqqa.

The announcement was part of an ongoing Turkish military operation it has dubbed “Euphrates Shield,” a push to drive ISIS and Kurdish militias out of northern Syria, which borders Turkey.

Turkey is demanding instead that the liberation happen any other way than with YPG forces. Meanwhile, according to one local report, the YPG are ready to move on surrounding Raqqa.

The U.S. push to distinguish between the use of YPG forces outside the city, rather than in the city center, buys the U.S. time to sort out how exactly the campaign for Raqqa will happen.

“What this sounds like is that the U.S. is stalling. The U.S. wants some ground movement against Raqqa in support of Mosul operations. The U.S. doesn’t have it so it is doing what it can in the meantime before another administration takes power,” Jennifer Cafarella, a Syria expert at the Washington-based Institute for the Study of War, explained to The Daily Beast.

On Wednesday, Army Lt. Gen. Stephen Townsend, the commander of U.S. forces in Iraq and Syria, announced that the YPG would be part of the initial war for Raqqa saying: “The only force that is capable on any near frame—near-term timeline is—are the Syrian Democratic Forces, of which the YPG are a significant portion.”

Earlier this week, Secretary of Defense Ash Carter said the Raqqa campaign would begin “within weeks,” but did not differentiate between isolating and liberating the city in an interview with NBC News.

Townsend said that the plan for Raqqa must start soon, in part, because ISIS is planning attacks on the West from Raqqa, but he said he did not know the specifics of such an attack.