The U.S. assessment is not contained in a formal document, said a source, who emphasized the cause of the deadly crash remains under investigation.

A preliminary report released last week included detail about the fuel, saying that the fuel to the plane's engines appeared to have been shut off.

Some shocking evidence has been found from the wreckage of Air India's plane AI171, which crashed within seconds of taking off in Ahmedabad on June 12. The rear part (tail) of the plane was not burnt in the fire, which shows signs of electric fire.