The US will maintain an open-ended military presence in Syria to ensure the enduring defeat of the jihadist group Islamic State, counter Iranian influence, and help end the civil war.
Secretary of State Rex Tillerson said President Donald Trump did not want to “make the same mistakes” that were made in 2011, when US forces left Iraq.
The US has about 2,000 troops in Syria.
Mr Tillerson denied the US was training a Kurdish-led border force, but Turkey accused it of sending mixed signals.
“US officials have made statements that refute one another,” said Turkish Prime Minister Binali Yildirim, whose country fiercely opposes such a move.
“One day it was said that a new border force had been set up, another day they said they are setting up a unit with local forces in order to maintain security in the region after eliminating Daesh [Islamic State group, or IS] in the region. These are all confusing statements.”
The US secretary of state said officials had “misspoke[n]” when they said the US was planning to set up a 30,000 strong “border security force” in northern Syria underpinned by the allied Kurdish-led Syrian Democratic Forces (SDF) militia.