US troops who were photographed in Syria wearing the emblem of a Kurdish armed group on their uniforms have been ordered to remove the patches, a military spokesman said.
The Americans, part of a US-led coalition battling the Islamic State of Iraq and the Levant (ISIL) group, were working alongside a coalition of Kurdish and Arab troops north of ISIL's de-facto capital Raqqa, and wore the insignia of the People's Protection Units (YPG).
"Wearing the YPG patches was unauthorised and it was inappropriate - and corrective action has been taken," US Colonel Steve Warren said on Friday. "And we have communicated as much to our military partners and our military allies in the region."
The images of the special forces soldiers - published by the AFP news agency - upset Turkey, which considers the YPG a "terrorist" group.
Turkish Foreign Minister Mevlut Cavusoglu denounced the US as "two-faced" and said the badges were "unacceptable".
"It is unacceptable that an ally country is using the YPG insignia. We reacted to it. It is impossible to accept it. This is a double standard and hypocrisy," Cavusoglu said.
Ankara also raised the issue with the US State Department.
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Al Jazeera's Alan Fisher, reporting from Washington DC, said "the US army [is] taking immediate steps to try to diffuse what could have become a diplomatic incident".
The troops were supporting the Syrian Democratic Forces (SDF), which is headed by the YPG, in an offensive against ISIL, also known as ISIS, in Raqqa province.
The US says it has about 300 soldiers serving in training and support roles in Syria and has acknowledged that they work with the SDF.
NATO member Turkey regards the YPG as an extension of the outlawed Kurdistan Workers Party, or PKK, which has fought for autonomy in Turkey's largely Kurdish southeast for three decades.
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Washington considers the PKK "terrorists", but backs the YPG in the fight against ISIL.
On Friday, US State Department spokesman Mark Toner declined to discuss the photos, saying he did not want to talk about where they were located in Syria.
"We understand Turkey's concerns, and let me make that clear," Toner said. "And we continue to discuss this as well as other concerns that Turkey has regarding [ISIL]."
Asked at a briefing on Thursday if it was appropriate to wear such insignia, Pentagon press secretary Peter Cook said that when Special Forces operate in some areas, they do what they can to blend in with the community to enhance their own security.
Source: Al Jazeera and agencies