Colonel Sean Ryan, spokesman for the US-led coalition fighting Islamic State, said the process of removing troops for the country had started.
But the Baghdad-based official did not give details and it is unclear how many vehicles or troop units had been withdrawn.
“Out of concern for operational security, we will not discuss specific timelines, locations or troops movements,” he said in a statement.
The news follows weeks of confusion over Donald Trump’s plans for US withdrawal from the country.
It was announced that the 2,000 troops in Syria would be withdrawn over the course of 60 to 100 days, but officials including US national security adviser John Bolton have said the US States will not leave until IS is defeated.
President Trump shocked almost everyone – from Congress and the Pentagon, to America’s allies and enemies around the world – when he announced the pullout, arguing that the US was “getting nothing” from its involvement in the country.
The announcement was criticised by British defence minister Tobias Ellwood, who said IS had “morphed into other forms of extremism” and that the threat “is very much alive”.
The US-backed, Kurdish-led Syrian Democratic Forces (SDF) said the move had “dangerous implications” for stability, would “negatively affect the campaign against terrorism” and create “a political and military vacuum”.
The Failing New York Times has knowingly written a very inaccurate story on my intentions on Syria. No different from my original statements, we will be leaving at a proper pace while at the same time continuing to fight ISIS and doing all else that is prudent and necessary!…..
— Donald J. Trump (@realDonaldTrump) 7 January 2019
In the weeks following his announcement, Mr Trump has given differing signals over the future of US involvement in the country.
After initially tweeting that he would bring back US troops “now”, Mr Trump this week said the US would “be leaving at a proper pace” while “continuing to fight IS and doing all else that is prudent and necessary”.
The news that a withdrawal had begun was confirmed on Thursday by the Syrian Observatory for Human Rights, based in the UK, which monitors activity in the war-town country through a network of activists.
It said a convoy of ten armoured vehicles and some trucks had pulled out of Rmeilan, in Syria’s north west, into Iraq.