ANKARA, Dec 3 (Reuters) - A Turkish plane that crashed last week killing all 57 people on board veered sharply from its route just before the disaster but the reason remains a mystery, civil aviation officials said on Monday.

The plane, belonging to private AtlasJet Airlines, crashed into a mountainside near the town of Isparta in central Turkey in the early hours of last Friday.

"According to the results of our preliminary investigation, the plane definitely deviated from the normal flight path," Ali Ariduru, general manager of Turkey's civil aviation authority, told a televised news conference.

Ariduru said there was no evidence of any technical problems or of any fire on board before the crash and weather conditions were normal. He also ruled out sabotage.

"It seems the plane had no problems, the engines were working fine until the crash ... The technical investigation at the scene is still continuing," he said, adding that the plane's "black boxes" or data recorders were also still being studied.

The 165-seat MD 83 plane, manufactured by McDonnell Douglas, had been flying to Isparta from Istanbul with 50 passengers and seven crew.

(Reporting by Inci Ozturk; Editing by Giles Elgood)

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