NEW DELHI, July 14 (Reuters) - A preliminary investigation into the crash of an Air India passenger jet last month that killed 260 people raises additional questions about the incident and the investigation is far from over, Air India's CEO said in a memo on Monday.

All mandatory maintenance tasks, including the pilots clearing the pre-flight breath analyser, had been completed, preliminary report identified no “mechanical or maintenance issues with the aircraft or engines,

An Air India executive is still urging its staff not to jump to any conclusions as the investigation into the crash that killed 260 people last month continues. A preliminary report into the June crash found that the plane's fuel control switches had been flipped off one by one.