U.S. intelligence indicates that a Turkish warplane shot down by Syrian forces was most likely hit by shore-based antiaircraft guns while it was inside Syrian airspace, American officials said, a finding in tune with Syria's account and at odds with Turkey.

The Turkish government, which moved tanks to the Syrian border after the June 22 incident, says the debris fell in Syrian waters, but maintains its fighter was shot down without warning in international airspace. Ankara also has said the jet was hit too far from Syrian...