Photos of U.S. special forces wearing the insignia of the Syrian Kurdish Protection Units (YPG) drew ire from Turkish President Recep Tayyip Erdoğan, who has repeatedly accused the militia of being linked to the terrorist group known as the Kurdistan Workers’ Party (PKK).

The Obama administration considers the YPG force, the armed wing of the Kurdish Democratic Union (PYD) that controls large swathes of northern Syria, one of the most effective partners fighting the Islamic State (ISIS/ISIL) on the ground.

Meanwhile, the communist separatist PKK, largely based in Turkey, has been deemed a terrorist group by both Washington and Ankara.

U.S. NATO ally Turkey has long considered the PYD and YPG to be the terrorist PKK’s Syrian offshoots.

“This is not what was promised to us,” Erdoğan said on Saturday, according to Hurriyet Daily News.

“I am someone who believes that politics should be conducted honestly. Therefore, our allies, those who are with us in NATO, cannot and should not send their own soldiers to Syria, with insignias of the YPG,” he also said, adding, “Those who say ‘we will continue to support YPG,’ come and learn from us. We tell them, we give the documents on the terror groups, but they take the wrong steps.”

The Turkish President accused the Obama administration of sending mixed messages when Secretary of Defense Ash Carter told lawmakers that the Syrian Kurdish groups were, in fact, associated with the PKK.

Hours after Carter made those comments, President Barack Obama’s State Department reiterated that the administration does not consider the PYD and YPG to be terrorist groups, stopping short of explicitly saying that the two groups are not linked to the PKK.

Former Republican presidential candidate and national security hawk Sen. Lindsey Graham (R-SC), as well as some Christian Assyrian groups in northern Syria, have echoed Turkey in accusing the Syrian Kurds of being allies of the PKK.

The photos of the armed U.S. service members in the northern Syrian province of Raqqa wearing the YPG patch on their uniform were released by Agence France-Presse (AFP).

Initially, Pentagon officials sought to play down the diplomatic tensions with Turkey over the YPG insignia pictures, arguing that it is common for U.S. special forces to wear the patches of their allies.

“Special operations forces when they operate in certain areas do what they can to, if you will, blend in with the community to enhance their own protection, their own security,” Peter Cook, the Pentagon press secretary, told reporters on Thursday.

The YPG insignia is a “sign of partnership,” Army Col. Steve Warren, a Baghdad-based spokesman for the U.S.-led coalition against ISIS, said on Twitter:

However, the following day, Col. Warren declared that wearing the YPG patch is “inappropriate.”

“Wearing those YPG patches was unauthorized and inappropriate, and corrective action has been taken,” Warren told Pentagon reporters Friday, adding, “We have communicated as much to our military partners and military allies in the region.”

Col. Warren cited “political sensitivities” around the issue as the reason why it was “inappropriate” for U.S. troops to wear the insignia.

He added:

The sensitivities, in fact, are with a NATO ally. So you’ve got to understand, these guys on the ground do what they’re going to do and they have their customs and courtesies that they have been following for years. But it’s also important to understand the larger strategic context, which — and I think that’s the inappropriateness of it — is that they didn’t understand that or appreciate it as they should have. …We’ve made the correction, so everybody’s moving on.

Mark Toner, a State Department spokesman, added that the Obama administration understood Turkey’s concerns over the YPG, which the Turkish President has linked to terrorist attacks in Ankara.

“We understand Turkey’s concerns, let me make that clear, and we continue to discuss this as well as other concerns Turkey has,” Toner told reporters Friday.

Nevertheless, Toner maintained that the administration does not regard the YPG as part of the PKK.

“With respect to Turkey’s comments about these photos we’ve been very clear … about our belief that the YPG is not connected to the PKK,” he said, adding, “On the contrary, we believe the YPG as well as other forces in northern Syria are effectively taking the fight to ISIL.”