(CNN) 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.
On Sunday, Erdogan said the offensive would go 30-35 kilometers into Syrian territory. Turkish-led forces had seized control of Ras Al Ain, he told reporters, while Turkish-backed troops had taken control of 109 square kilometers.
"We are not allowing the establishment of a terror state in northern Syria, and we will not in the future," Erdogan said. "We have no interest in other countries land, however those that set eyes on our lands, we cannot close our eyes/overlook, we don't have the luxury of showing mercy."
There have been 652 attacks on civilians by the PKK/YPG-PYD, he said. "490 terrorists have been neutralized thus far. 440 have been killed, 26 wounded, and 24 surrendered."
"Since when a nation has sat down at the table with a terrorist organization?," Erdogan asked in the press conference.