ISTANBUL — Sporadic fighting continued in northern Syria on Friday, casting uncertainty over an American-brokered truce, as conflicting reports emerged about whether Kurdish forces were retreating or hunkering down and whether Turkish troops were advancing or holding fire.

Clashes continued on and off in the vicinity of a strategic Syrian border town, despite President Trump hailing the cease-fire, announced on Thursday night by Vice President Mike Pence, as “an incredible outcome.”

Mr. Pence had promised that fighting would halt for five days to allow Syrian Kurdish forces to evacuate a central pocket of northern Syria that Turkey wants to wrest from Kurdish control.

But though fighting eased, gunfire could still be heard in the area of Ras al-Ain, a town next to the Turkish-Syrian border, during the early morning and early afternoon. By nightfall the Kurdish military leadership said its forces remained in a “defensive position” in the places they had been deployed when the cease-fire was agreed — contradicting Turkish and American claims that they had started to retreat, as required by the terms of the deal.