The official said the movement of equipment is part of what the military calls the start of a "deliberate withdrawal" from Syria, where about 2,000 troops have been working with a coalition of Syrian Kurdish and Arab fighters to defeat the remnants of the Islamic State group.
Col. Sean Ryan, spokesperson for the coalition fighting the Islamic State in Iraq and Syria, said the USA started "the process of our deliberate withdrawal from Syria".
A convoy of ten USA military vehicles was seen leaving a base in Hasakah province in northeast Syria and heading towards the Iraqi border, according to the Syrian Observatory for Human Rights.
Global players in the conflict have been in talks about the future of former USA territory in Syria.
The reports could not be independently confirmed.
A Defense Department spokesperson later said that while equipment was being moved out of Syria, troops were not withdrawing.
The U.S. has begun to withdraw equipment from Syria as questions about President Donald Trump's timeline and strategy for pulling troops from the eight-year conflict there continue to fuel confusion.
The US says it has begun the process of withdrawing from Syria but Russian Federation cast doubt on the claim Friday, saying it thinks Washington wants to stay in the Arab country. But that time frame has since been extended several times.
Huawei employee arrested over alleged spying
Huawei said in a terse statement that it was "aware of the situation" and "looking into it" and had no further comment for now. A Huawei employee was arrested in Poland on Tuesday and charged with spying for China, according to numerous media reports .
Ilham Ahmed, who co-chairs the USA -backed Syrian Democratic Council in northeast Syria, said the Americans have a right to make decisions that are in their country's security and national interests. "That framework is conditions-based and will not subject troop withdrawal to an arbitrary timeline".
USA forces' vehicles and structures are seen on the outskirts of the northern Syrian town of Manbij on December 26, 2018.
But even as the SDF advance, there are growing concerns about their safety.
"The return of official control over all Kurdish-populated territories should also neutralize the security risks to Syria's neighbors", she added, in an apparent reference to Turkey, which has been threatening to cross its southern border into Syria to attack Kurdish armed groups there.
The Syrian Observatory also reported that the SDF is bolstering its forces on the border with Turkey "in anticipation of any surprise attack".
"When the time and place comes, the terrorists here will also be buried in the ditches and trenches they have dug", he said. "Our preparations are continuing intensively".
Turkish Foreign Minister Mevlut Cavusoglu said he will carry out the long-planned offensive against the YPG, regardless of the US withdrawal pace.
Why it matters: Bolton's insistence that the United States still stop the re-emergence of the Islamic State and Iranian-backed proxies in Syria could frustrate military planners trying to interpret Trump's withdrawal order.