The US-led military coalition in Syria has begun the process of withdrawing troops, an American military official said.
Colonel Sean Ryan, spokesman for the coalition fighting the so-called Islamic State (IS) group, said the US had started "the process of our deliberate withdrawal from Syria".
"Out of concern for operational security, we will not discuss specific timelines, locations or troop movements," he said in a statement.
An official said the equipment withdrawal is underway and an unspecified number of additional US troops have been moved into Syria to assist with the withdrawal process, including to provide additional security.
The Britain-based Syrian Observatory for Human Rights, which monitors the conflict in Syria through a network of activists on the ground, said the withdrawal began on Thursday night.
It said a convoy of about 10 armoured vehicles and some trucks pulled out from Syria's north-eastern town of Rmeilan into Iraq.
Confirmation of the first withdrawals comes amid confusion over plans to implement President Donald Trump's pullout order and threats from Turkey to attack the Kurds, who have been America's partners on the ground in the war against IS in Syria.
There are 2,000 American troops in Syria. Mr Trump's decision in December to pull them out, declaring in a tweet the defeat of IS, sent shockwaves across the region and led to the resignation of US Defense Minister James Mattis and the top US envoy to the anti-IS coalition.
During a surprise visit to Iraq over Christmas, Mr Trump reiterated his beliefs that the job in Syria is done.
It also led to major criticism that the US was abandoning its Kurdish allies amid Turkish threats of an imminent attack.
On Sunday, US national security adviser John Bolton said American troops will not leave north-eastern Syria until IS is defeated and American-allied Kurdish fighters are protected.
Secretary of state Mike Pompeo, who is on a tour of the region, has also sought to reassure the Kurds that they will be safe after US troops withdraw from the country.
"These have been folks that have fought with us and it's important that we do everything we can to ensure that those folks that fought with us are protected," Mr Pompeo said of the Kurds while visiting Irbil, the capital of Iraq's semi-autonomous Kurdistan region, after talks in Baghdad.