US-backed Syrian Democratic Forces say a prominent politician, her driver, members of Kurdish security forces and several civilians were killed by Turkish-backed militants in Syria on Saturday, after videos circulating online appeared to show the killings.
The Turkish-backed Free Syrian Army or FSA (also called the Syrian National Army), have denied those claims. CNN cannot independently verify the videos.
A video circulating on social media purports to show the bullet-riddled SUV of Secretary-General of the pro-Kurdish Future Syria Party, Hevrin Khalaf, surrounded by several men wearing what appears to be military fatigues.
In a separate video, a body of a woman -- believed to be Khalaf -- is seen lying in rubble with her face and hair covered in dust. At least one man can be seen standing over her and filming. He taps the body with his feet and says, "this is the corpse of pigs." The video is filmed up close and little else can be seen in the clip.
Local journalist Ousama Muhammed, who knows Khalaf, told CNN that the vehicle belongs to her. Meanwhile, the Syrian Democratic Council -- the political wing of the SDF (who led the charge in defeating ISIS in Syria) -- blamed Turkish-backed militias in a statement on Khalaf's death.
"She was taken out of her car during a Turkish-backed attack and executed by Turkish-backed mercenary factions on the International Road between Qamishlo and Manbij, with her driver who was also martyred," the statement said.
Turkish media reports that Khalaf had been killed by aerial bombardment. CNN cannot independently verify how or where Khalaf died.
Several other videos posted online appear to show at least one man on a roadside with his hands tied in northern Syria, whose lifeless body is being fired upon as a man cries out in Arabic "film me shooting him with a sniper rifle" and "pigs...prisoners..kill them."
A media activist on the scene told the New York Times that two men who appeared in the former video -- the one who is dead, and another who appears in that clip alive -- were both killed by a faction allied with the Turkish-backed FSA militia in northern Syria on Saturday.
The New York Times says the militant group Ahrar al-Sharqiyah entered Syria from Turkey and took control of this area of the M4 highway where the killings happened.
The Turkish-backed FSA denies that it was involved, saying none of their forces or factions have reached the M4 highway where the killings happened.
"Our forces haven't reached M4 road, we reached only 712. PYD is saying that she was killed on M4 road, it is known that that road is being bombed and shelled with artillery, this is the first thing," said National Army spokesman Major Yousef Hamoud. "Secondly, it might be an internal job due to a disagreement between political parties that belong to SDF."
The FSA said in a separate statement that they emphasize their "obligation to follow third Geneva Convention 1949 about the treatment of war prisoners and their rights" and said if there had been any violation, it would "follow it up, investigate and hold accountability and search for those who are participating and turn them into the martial judiciary system immediately."
SDF Press Commander Marivan Qamishlo told CNN that as many as 11 people, including Khalaf, were executed in the same area.
"Nine civilians were executed at the M4 location and two members of the 'Asayish' Kurdish internal security forces at a small check point", says Qamishlo.
He added that politician Khalaf was among the civilians killed, but not at the same time.
"Asayish Kurdish security forces members were killed before Hevrin Khalaf arrived to the checkpoint," said the SDF Press Commander.
The UK-based monitoring group, Syrian Observatory for Human Rights (SOHR), also says that Turkey-backed groups killed nine civilians on the same highway, including Khalaf. They do not specify their sources.
It comes days after Turkish President Recep Tayyip Erdogan launched the incursion into Syria to drive Kurdish forces away from the border and to use the area to resettle around 2 million Syrian refugees. The SDF who operate in the area are US allies, and are led by the Kurdish People's Protection Units (YPG), which Turkey considers a terrorist organization.
Turkish forces cut off Kurdish city of Kobani
On Sunday Turkish forces and the Syrian rebels fighting with them cut off the main road between the West and East of Syrian Kurdish territory, effectively cutting off the main city of Kobani.
CNN witnessed Turkish military armored personnel carriers on the M4 highway between Tal Tamr and Ain al Issa, parked by the side of the road. Further reinforcements made their way through the dust towards the dozen armored vehicles, parked 10 meters (about 30ft) from the road.
This was preceded by Turkish-backed Syrian rebels blocking off the highway just past Ain Al Issa, using a checkpoint, according to a US official.
CNN did not observe the checkpoints, but did hear gunfire on the highway which caused civilians to flee in panic.
While Kurdish civilians fear the Syrian rebels, some are also furious at US and Coalition forces, with whom they fought ISIS, for abandoning them. "God curse America," said one man.
The arrival of Turkish forces on the M4 highway, also known as the international road, suggests the ambitions of Ankara are much wider than initially stated.
The Turkish patrol was about 30 miles into Syrian Kurdish-held territory, and the Syrian rebel checkpoints, in areas where the Turkish were not thought to have ambitions. The move also cuts off the main highway -- and perhaps only route -- to Kobani, where US troops are based.
CNN also witnessed the departure from Ain al Issa of an American patrol.
The four armored vehicles left minutes before a Turkish jet flew very low over the town, "buzzing" the Syrian Kurdish fighters in it and the American convoy.
Two US Apache helicopters then flew over the town for 15 minutes, looping what is a key base for the SDF.
CNN's Bianca Britton wrote from London. Arwa Damon, Jennifer Deaton, Sharif Paget, Scott McWhinnie and Braden Goyette contributed reporting.