A cockpit voice recording of doomed Air India Flight 171 indicates the younger co-pilot asked his more experienced colleague why he turned off the plane’s fuel-supply switches, according to people familiar with the matter.

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.

India's aircraft accident investigation body said on Thursday it was too early to reach any "definite conclusions" on what led to the deadly Air India Boeing plane crash last month that killed 260 people.