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 Wall Street Journal reports.

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 territory to have been engaged by an antiaircraft gun.

Damascus has said it shot down the plane with an antiaircraft battery with an effective range of about 1.5 miles.

"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. The senior U.S. defense official cautioned that much remains unknown about the incident.

A Turkish official said he wasn't aware of the American doubts, and reiterated the government's position that a Syrian missile downed the plane in international airspace.

The downing of the jet spurred fears of a widening regional conflict and led the North Atlantic Treaty Organization, following a presentation by Turkey, to condemn Syria's action.

The use of antiaircraft fire would suggest the Turkish plane was flying low to the ground, and slowly, U.S. officials said - though Syria said the jet was traveling at 480 miles an hour. If hit by antiaircraft fire, the jet likely came closer to the Syrian shoreline than Turkey says, U.S. officials said.

According to the Journal, 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.

A former senior U.S. official who worked closely with Turkey said he believed the flight's course was meant to test Syria's response. "You think that the airplane was there by mistake?" the former official said.

"These countries are all testing how fast they get picked up and how fast someone responds," said a senior U.S. official. "It's part of training."