Turkey's invasion of northeastern Syria began Wednesday after President Donald Trump ordered U.S. troops to pull back from the area to clear the way for Turkish forces.
U.S. forces were preparing to withdraw from northeastern Syria Sunday as hundreds of Islamic State group supporters escaped from a displacement camp amid reports of alleged atrocities as Turkish forces continued their advance.
The U.S. is "preparing to evacuate" about 1,000 troops from the area "as safely and quickly as possible," Defense Secretary Mark Esper told CBS' "Face the Nation," according to an excerpt of an interview set to air Sunday.
Esper said that the conflict between Turkish forces and U.S.-backed Syrian Kurdish fighters had become "untenable" for the U.S. military.
U.S. allies have urged an end to the Turkish invasion, which sparked fears of a renewed humanitarian crisis in the region and a resurgent ISIS threat.
President Donald Trump said Sunday that it was "very smart not to be involved in the intense fighting along the Turkish Border, for a change."
He added that he was working with Congress on imposing "powerful sanctions on Turkey."
But Trump has largely stood by his decision to pull U.S. troops back to clear the way for Turkish forces, acknowledging late Saturday that he was an "island of one" on the issue.
The U.S. previously set down red lines for the Turkish offensive that would trigger economic sanctions, including ethnic cleansing and indiscriminate fire directed at civilian populations.
The Kurdish-led Syrian Democratic Forces (SDF) and Syrian Observatory for Human Rights said early Sunday that close to 800 members of a camp holding the families of ISIS fighters had escaped after Turkish shelling.
Some Kurdish guards were forced to leave their posts as fighting neared a camp for displaced people near the town of Ain Eissa, a spokesperson for the U.K.-based observatory told NBC News.
"It's now chaos in the camp and there are people still escaping," Rami Abdulrahman said.
NBC News has been unable to independently verify the claim.
The Turkish military and Turkey-backed Syrian fighters continued to advance toward Ain Eissa, the administrative center of the Kurdish-held areas.
As they drove forward, video and photographs appearing to show alleged atrocities carried out by Turkish-backed fighters spread on social media.
Multiple U.S. officials told NBC News the video, which appeared to show the execution of a Kurd, appeared to be genuine.
The video is disturbing and NBC News has blurred the most graphic images.
The Syrian Observatory for Human Rights also claimed some civilians had been executed. NBC News has been unable to independently verify the claim.
U.S. allies in Europe sought to step up the pressure on Turkey, with both Germany and France saying they will halt weapons exports to Ankara.
British Prime Minister Boris Johnson expressed "grave concern about Turkey's military operation in northern Syria" in a call with Turkish President Recep Tayyip Erdogan Saturday, his government said.
Protests in support of the Kurds were held in Greece, Germany and France Saturday. Demonstrators also gathered outside the White House Saturday holding large Kurdistan flags.
Former Defense Secretary James Mattis, who led the Pentagon through the first two years of the Trump administration, warned during an exclusive interview with NBC's "Meet the Press" Saturday that the president's decision to pull troops from Syria's border in advance of a Turkish incursion could have dire consequences and lead to ISIS's resurgence.
U.S. troops stationed in the region also came under artillery fire from Turkish forces late Friday, but no Americans were injured in the incident.
"There will be serious consequences for our national security well beyond Syria,"said Brett McGurk, former special presidential envoy for the global coalition to defeat ISIS and NBC News foreign affairs analyst, in response to Sunday morning's news.
"For now, may our people get out safely."
World leaders and aid organizations have warned the offensive could lead to a new humanitarian crisis on the ground.
The United Nations said Sunday that more than 130,000 people have been displaced from rural areas around the strategically key northeastern Syrian border towns of Tel Abyad and Ras al-Ayn as a result of fighting between Turkish-led forces and Kurdish militia.
It estimated up to 400,000 civilians in the Syrian conflict zone may require aid and protection.
The Trump administration also released $50 million in assistance to Syria late Saturday "to protect persecuted ethnic and religious minorities," according to a statement from White House Press Secretary Stephanie Grisham.
Turkish troops are fighting the Syrian Democratic Forces, which are led by the Kurdish People's Protection Units (YPG). Turkey views the YPG as an extension of the separatist Kurdistan Workers' Party (PKK), which is considered a terrorist group by the United States.
But the Kurdish-led Syrian Democratic Forces have been crucial U.S. allies in the war on ISIS.
The SDF has held more than 10,000 ISIS members in detention centers and prison camps, but they said they are being forced to abandon some of those positions to fight the Turkish invasion.
Turkey's defense ministry said Sunday that 480 "terrorists" have been killed since launching its military operation. That claim has not been independently verified by NBC News.
The number of casualties since the violence began has varied between sources and NBC News has been unable to independently verify any claims.