The video appears to be the first evidence of US special forces cooperating with Turkish troops in their battle against Islamic State (Isil).
The incident illustrates the complex web of alliances and enmities in Syria, where many of America’s allies are fighting each other and some rebel groups that receive US support still harbour strong anti-American sentiments.
The footage shows a crowd of rebel fighters in the town of al-Rai near the Turkish border, which was captured from Isil by Syrian rebel groups with the backing of Turkey. Turkey, which launched a military incursion into Syria in late August, has been backing the FSA.
“Christians and Americans have no place among us,” shouts one man in the video. “They want to wage a crusader war to occupy Syria.”
Another man calls out: “The collaborators of America are dogs and pigs. They wage a crusader war against Syria and Islam. ”
The US troops are not wearing traditional uniform but they carry American weapons and are wearing the distinctive round helmets favoured by US special forces.
Another video shows the US troops looking nonchalant and waving at the camera even as some of the rebels tell them to leave.
“Heated tempers and YPG relations aside, this was a big mistake by FSA. But it does go to show the diplomacy now required to make it work,” he said.
Turkey is vehemently opposed to the YPG and its FSA proxies have fought with Kurdish fighters even though they are in theory both US allies committed to fighting together against Isil.
It was not clear if the confrontation in al-Rai was spontaneous or ordered by senior FSA figures or even their Turkish allies.
The US troops are believed to have been operating alongside Turkish forces in northern Syria. Video footage shows the American trucks sharing a road with Turkish tanks.
A spokesman for US Central Command said they were aware of the video and looking into the incident.