U.S. forces began pulling out of their largest base in northeastern Syria on Monday, three Syrian military and security sources said, part of a wider departure as the U.S.-allied government in Damascus consolidates control.

Dozens of trucks, some carrying armored vehicles, departed the base at Qasrak in Hasakah province on Monday morning, witnesses said. Reuters footage later showed the trucks moving along a highway on the outskirts of the city of Qamishli.

The U.S. military's Central Command (Centcom) did not immediately respond to an emailed request for comment.

A full withdrawal from Qasrak would still leave the U.S.-led coalition with a base in Rmelan, also known as Kharab al-Jir, near the Iraqi border.

Qasrak has been a main hub for the U.S.-led global coalition fighting Islamic State in Syria, where U.S. troops deployed over a decade ago, partnering with the Kurdish-led Syrian Democratic Forces (SDF) against the jihadist group.

Neither the Syrian defense ministry nor the SDF responded to requests for comment.

One of the Syrian sources, a military official briefed on U.S. plans, said the pullout was expected to take about a month, but that it remained unclear whether the withdrawal from the base was temporary or permanent.

The second Syrian source, also briefed on U.S. plans, said it would take a number of weeks.

Since government forces under President Ahmed al-Sharaa seized control of swathes of the northeast from the SDF last month, U.S. forces have withdrawn from a base at al-Shaddadi in Hasakah province, and a garrison at al-Tanf, located at the intersection of Syria's border with Iraq and Jordan.

A senior U.S. official told Reuters on Wednesday that some U.S. troops were leaving Syria as part of a "deliberate and conditions-based transition."

The official said U.S. presence at scale was no longer needed given the Syrian government's "willingness to take primary responsibility for combating the terrorist threat within its borders."

The Wall Street Journal reported last week that the U.S. was withdrawing all of its roughly 1,000 troops from Syria.

Syria joined the U.S.-led coalition to combat Islamic State last year. The militant group, which once controlled a third of Syria and Iraq, claimed responsibility for two attacks on Saturday that killed a soldier and a civilian.