"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"
"We see no indication that it was shot down by a surface-to-air missile" as Turkey says, said a senior defense official. Officials declined to specify the sources of their information."
"Some current and former American officials believe Ankara has been testing Syrian defenses. The version of the Turkish F-4 Phantom that was shot down typically carries surveillance equipment, according to U.S. defense officials."