The White House has said the US military mission in Syria is coming to a "rapid end", but not announced a timetable for a full troop withdrawal.
A statement said the Islamic State (IS) group was almost completely destroyed, and that the US would consult its allies regarding future plans.
President Donald Trump declared last week that the US would "be coming out of Syria very soon".
But advisers reportedly persuaded him that would risk a jihadist resurgence.
A senior administration official told NBC News that the president had agreed at a meeting on Tuesday to keep troops in Syria for an undetermined period, but "wasn't thrilled about it, to say the least".
"The president made his displeasure clear about any kind of long-term presence in Syria," the official added.
The US has about 2,000 personnel on the ground in eastern Syria supporting an alliance of Kurdish and Arab militias called the Syrian Democratic Forces (SDF).
With the help of US-led coalition air strikes, SDF fighters have captured tens of thousands of square kilometres of territory from IS over the past three years.