Esper told reporters while traveling to the Middle East that about 1,000 troops leaving northern Syria will take weeks to reconstitute in Iraq. That presence will add to the 5,000 American forces already in that country.
U.S. troops worked alongside Kurdish fighters to expel the Islamic State out of northern Syria.
The Kurdish-led Syrian Democratic Forces also withdrew from a key border town in northeastern Syria as part of a cease-fire agreement between Turkey and the United States.
Vice President Mike Pence last week announced a cease-fire in that dispute after traveling to Turkey, but it remains uneasy at best. Esper said, though, it is holding, for the most part, allowing the Kurds to leave the region.
"We see a stabilization of the lines if you will on the ground," Esper said. "And we do get reports of intermittent fires, this and that. That doesn't surprise me necessarily."
Mazloum Abdi, leader of the Kurdish-led forces, said to reporters Saturday that Turkey is not allowing them to leave, while Turkey officials claimed there was "absolutely no impediments to withdrawal."
House Speaker Nancy Pelosi traveled to Jordan this weekend on a Syrian fact-finding mission to discuss other regional matters with King Abdullah II. She was joined on the trip with Reps. Adam Schiff, D-Calif.; Eliot L.Engel, D-N.Y.; and Mac Thornberry, R-Texas.
"Our bipartisan delegation is visiting Jordan at a critical time for the security and stability of the region," Pelosi said in a statement. "With the deepening crisis in Syria after Turkey's incursion, our delegation has engaged in vital discussions about the impact to regional stability, increased flow of refugees, and the dangerous opening that has been provided to [the Islamic State], Iran and Russia."