The US envoy to Syria said on Wednesday that there is evidence of war crimes being committed during the Turkish offensive in the north of the country, while videos emerged on social media of apparent atrocities.

"We've seen several incidents which we consider war crimes," Jim Jeffrey told the House Foreign Affairs Committee.

Videos reviewed by Business Insider appear to show Turkish-backed Syrian rebels committing atrocities, killing men in civilian clothing, and boasting of their kills.

Turkey invaded on October 9, displacing thousands of Kurds, and shelling northern areas of the war-weary country. Turkish officials deny that war crimes have been committed.

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The US envoy to Syria said on Wednesday that there is evidence of war crimes being committed during the Turkish offensive in the north of the country, while videos emerged on social media of apparent atrocities.

"We've seen several incidents which we consider war crimes," Jim Jeffrey, Donald Trump's special representative to Syria told the House Foreign Affairs Committee.

Turkey invaded northern Syria on October 9, displacing thousands of Kurds, and shelling vast areas of the war-torn country. Turkish officials deny that war crimes have been committed, calling such allegations a "smear campaign."

Multiple videos posted to social media reviewed by Business Insider this week appear to show Turkish-backed Syrian rebels committing atrocities, posing with victims, and boasting of their kills.

Business Insider has decided not to publish any of the footage.

The US envoy to Syria, Jim Jeffrey, speaking to the House Foreign Affairs Committee on Wednesday. C-SPAN

Two videos, CNN reported, show the bullet-riddled bodies of Kurdish politician and activist Hevrin Khalaf and her two bodyguards. In one, a man stands over her body and films himself.

According to CNN, he then says to the camera in Arabic: "This is the corpse of pigs."

In another, seen by Business Insider, men who appear to be Turkish-backed Syrian rebels taunt a man in civilian dress and then drag him by the neck to be executed as onlookers laugh.

General Mazlum Kobane, head of the Kurdish forces in Syria, warned NBC on Saturday the invasion of Syria "will be the biggest ethnic cleansing operation of the 21st century" which is "happening right in front of the American army's eyes."

Jeffrey didn't go so far as to confirm Kobane's prediction on Wednesday, saying: "We haven't seen widespread evidence of ethnic cleansing."

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"Many people fled because they're very concerned about these Turkish-supported Syrian opposition forces, as we are."

In this photo taken from the Turkish side of the border between Turkey and Syria, in Ceylanpinar, Sanliurfa province, southeastern Turkey, smoke billows from targets in Ras al-Ayn, Syria, caused by bombardment by Turkish forces, Tuesday, Oct. 15, 2019. Associated Press

Jeffrey also told the House Foreign Affairs Committee the US is investigating claims burning white phosphorus was used by rebel forces.

Read more: Video appears to show US troops being pelted with stones and rotten fruit as they pull out of Syria

The United Nations is also investigating, after apparent chemical burns were seen on a child caught in clashes between forces. It is illegal to use white phosphorus against civilians targets, but it is approved for use in warfare.

Local residents look on as a convoy of Turkish forces' trucks transporting tanks is driven on a road towards the border with Syria in Sanliurfa province, Saturday, Oct. 12, 2019. Associated Press/Lefteris Pitarakis

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US Defense Secretary Mark Esper acknowledged on Tuesday he'd seen evidence indicating war crimes had been committed in Syria.

"I think those responsible should be held accountable. In many cases, it would be the government of Turkey," he said.