The Trump administration’s internal debate over how to capture Raqqa, the so-called capital of the Islamic State (IS), is continuing nearly two weeks after the Pentagon presented the White House with a detailed blueprint on how to do the job.

The US Central Command remains strongly in favor of moving ahead with the Syrian Kurdish group known as the People’s Protection Units (YPG) and their Arab allies who operate under the umbrella of the Syrian Defense Forces (SDF). But concerns over Turkey, a critical NATO ally, are holding up plans to arm and train the SDF under the terms of a special presidential dispensation known as Section 1209 that permits the Pentagon to arm nonstate foreign militias. Turkey has repeatedly warned against giving the YPG modern sophisticated weapons, saying the group could transfer these to its ally, the Kurdistan Workers Party, which is fighting for autonomy inside Turkey.

Trump has not signed Section 1209 for the SDF yet even though the Obama administration recommended he do so. The announcement of a final decision on Raqqa has likely been put off until after Turkey votes in a referendum April 16 that would formalize the sweeping powers President Recep Tayyip Erdogan already wields. Washington is worried that Erdogan will use the issue to whip up further anti-Americanism and take further aggressive action against the YPG in Syria to boost nationalist votes.

Secretary of Defense Jim Mattis is said to be among those raising red flags over the long-term effects of acting in concert with a group that Turkey views as terrorists. “He’s thinking beyond Erdogan and focusing on the partnership with Turkey, and how this will impact relations in the long term,” said a senior administration official familiar with the debate. Some administration officials participating in the debate are arguing in favor of postponing Raqqa, saying that IS — under assault from all sides and its access to Europe via Turkey now cut off — no longer poses an immediate threat.