American soldiers pelted with fruit and vegetables as they exit northern Syria
Locals in the northeastern Syrian city of Qamishli pelted US vehicles with fruit and vegetables as they withdrew from the region in the wake of an offensive by Turkey.
Earlier this month, the White House announced it was withdrawing troops deployed in northeastern Syria, paving the way for Turkey's offensive against the Kurdish People's Protection Units (YPG), which Ankara considers a terrorist group.
The move has provoked anger from many in northern Syria who feel the US is abandoning an ally to the Turkish assault.
At a demonstration on Sunday evening, protesters held up placards slamming the US for its decision to withdraw.
“Tell your children that the children of the Kurds were killed by the Turks, and we did nothing to protect them," read one sign.
Turkey's nearly two-week old offensive has displaced some 300,000 people and led to 120 deaths among civilians and 470 among SDF fighters, the Syrian Observatory for Human Rights said on Sunday. Turkey says 765 terrorists but no civilians have been killed in its offensive.
Defense Secretary Mark Esper said on Monday that the Pentagon was considering keeping some US troops near oilfields in northeastern Syria alongside Kurdish-led Syrian Democratic Forces (SDF) to help deny oil to Islamic State (IS) group militants.
More than 100 vehicles crossed the border into Iraq early on Monday from the northeast tip of Syria.
As they arrived in Iraq's northern Kurdish city of Erbil, videos appeared to show locals throwing rocks at the vehicles.
Speaking to reporters during a trip to Afghanistan, Esper said that, while the US withdrawal was under way, some troops were still with partner forces near oil fields and there had been discussions about keeping some of them there.
He said that was one option and no decision had been made "with regard to numbers or anything like that". The Pentagon's job was to look at different options, he added.
"We presently have troops in a couple of cities that (are) located right near that area," Esper said.
"The purpose is to deny access, specifically revenue to ISIS (Islamic State) and any other groups that may want to seek that revenue to enable their own malign activities."
Donald Trump's shift has opened a new chapter in Syria's eight-year war and prompted a rush by Turkey and by the Damascus government and its ally Russia to fill the vacuum left by the Americans.
The US president's decision has been criticised in Washington and elsewhere as a betrayal of Kurdish allies who had fought for years alongside US troops in a region rich in oil reserves and farmland.
The New York Times reported late on Sunday that Trump was now leaning in favour of a new military plan to keep about 200 US troops in eastern Syria near the Iraq border. The White House did not immediately respond to a request for comment.
Turkey is seeking to set up a "safe zone" as a buffer against the YPG militia, the main component of the SDF. Ankara sees the YPG as a terrorist group due to its links to Kurdish insurgents in southeast Turkey.
Erdogan has said Ankara will resume its assault in Syria when the deadline expires on Tuesday if the SDF has not pulled back from its proposed zone, which spans much of the border.
"We will take up this process with Mr Putin and after that we will take the necessary steps" in northeastern Syria, Turkish President Recep Tayyip Erdogan told a forum in Istanbul hosted by broadcaster TRT World on Monday, without elaborating.
Erdogan has also said Turkey will set up a dozen observation posts in the "safe zone", prompting criticism from Iran.
"We are against Ankara's establishing of military posts in Syria," Iranian foreign ministry spokesman Abbas Mousavi told a weekly news conference broadcast live on state TV on Monday.
"The issues should be resolved by diplomatic means... Syria's integrity should be respected," said Mousavi, whose country is a staunch ally of Syrian President Bashar al-Assad.
Russian Defence Minister Sergei Shoigu was quoted as saying that Moscow, which is also allied with Damascus, hopes its coordination with the United States and Turkey will help security and stability in the region.
On Monday, Reuters video images showed armoured vehicles carrying US troops through the Sahela border crossing into Iraq's northern province of Dohuk.
About 30 trailers and Hummers carrying heavier duty equipment crossed, with troops in cars coming through, an Iraqi Kurdish security source said.
On Sunday, the SDF said they had withdrawn from the border town of Ras al-Ain under the US-brokered ceasefire deal, but a spokesman for Turkish-backed Syrian rebels said the withdrawal was not yet complete.
Turkish security sources said on Monday that Kurdish YPG forces were advancing towards Hasakah, which is south of the proposed safe zone, adding some 125 vehicles had already left. They also said more than 80 Kurdish militants had been captured alive or surrendered to Turkish forces.