"Our position in Syria has been to defeat ISIS," Pentagon spokeswoman Dana White told reporters, using an acronym for the Islamic State group.

"That mission has not changed," she added.

Trump set establishment alarm bells ringing Tuesday when he said he wants US troops to "get out" of Syria.

Many of his top aides worry a premature pull-out would have far-reaching negative consequences.

The White House on Wednesday vowed the US mission in Syria would come to a "rapid end," but failed to put a timetable on an eventual withdrawal.

Another Pentagon spokesman, Lieutenant General Kenneth McKenzie, also said the military policy remains the same.

"We've always thought that as we reach finality against ISIS in Syria we are going to adjust the level of our presence there, so in that sense nothing actually has changed," he said.

The United States has since late 2014 led a global coalition against IS in Syria and Iraq, but steady gains against the group have stalled in recent weeks as US-backed Kurdish fighters have switched their focus from battling the jihadists to fighting Turkish troops in the Afrin area.

McKenzie declined to comment when asked why the Kurds would want to keep fighting IS for America when Trump has signaled his willingness to leave Syria.