US special operations troops are fighting against the Islamic State on the frontlines as part of a major Kurdish-led offensive against the group's Syrian headquarters in Raqqa.
The American troops were photographed by an AFP photographer traveling with the Kurdish-led and dominated Syrian Democratic Forces (SDF), which the US is aiding in its fight against the Islamic State. Video of the commandos also circulated on social media.
Photos and video showed the men in full combat gear riding in a pickup truck mounted with an automatic grenade launcher. AFP reported that the men were also positioned on top of a house and using anti-tank weapons to destroy suicide vehicle bombs approaching the SDF positions.
The men may be part of the group of 250 American commandos that the Pentagon announced earlier this year would be sent to Syria to aid the fight against the Islamic State.
US advisors have been assisting the Kurds and other groups fighting the Islamic State and Syrian President Bashar al-Assad's regime in Syria, but this is the first time US troops have been documented taking part in the fighting on the ground against the Islamic State in an offensive manner. American warplanes have been bombing IS positions in support of the SDF and other Syrian groups for months.
The US troops are shown in the video wearing American flags on the chest plate of their body armor, but their arm patch, usually reserved for an American unit insignia, instead bears the emblem of the Kurdish YPG militia, which is considered an offshoot of the Turkey-based Kurdish PKK. US ally and NATO member Turkey has designated the PKK a terrorist organization and is currently embroiled in a violent war with the group in southeastern Turkey — a war which occasionally spills over the border into YPG territory in Syria.
Turkish Foreign Minister Mevlut Cavusoglu reacted angrily to the photos.
"It is unacceptable that an ally country is using the YPG insignia," he said. "We reacted to it. It is impossible to accept it. This is a double standard and hypocrisy."
The US Defense Department played down the significance of the patches.
"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," Pentagon press secretary Peter Cook said.
Turkey is concerned by Kurdish advances along its border, where the YPG already controls an uninterrupted 250-mile stretch.
The United States commandos were shown helping the SDF and YPG in its battle against Islamic State farther east, in Hasaka and Raqqa provinces.
The YPG has driven IS from wide areas of northern Syria over the last year or more, though its advances have recently slowed. There has been no indication of when a full assault on Raqqa city might take place.
Reuters contributed to this report.