By Sakshi Dayal and Allison Lampert

NEW DELHI (Reuters) -Investigators have downloaded flight recorder data from an Air India crash this month that killed 260 people, India's civil aviation ministry said on Thursday, a long-awaited step towards understanding the world's worst aviation disaster in a decade.

The London-bound Boeing 787 Dreamliner crashed moments after takeoff from India's Ahmedabad city on June 12, killing 241 of the 242 people on board and the rest on the ground.

The black boxes of the plane - the cockpit voice recorder (CVR) and flight data recorder (FDR) - were recovered in the days that followed, one from the rooftop of a building at the crash site on June 13, and the other from the debris on June 16.

The ministry said data from the front recorder was accessed on Wednesday by a team led by India's Aircraft Accident Investigation Bureau, with the U.S. National Transportation Safety Board.

"These efforts aim to reconstruct the sequence of events leading to the accident and identify contributing factors to enhance aviation safety and prevent future occurrences," the ministry said in a statement.

The probe into the crash of the Air India plane, which started losing height after reaching an altitude of 650 feet, includes a focus on engine thrust, according to a source with knowledge of the matter.

The Wall Street Journal has reported that investigators believe the Dreamliner had its emergency-power generator operating when it crashed. 

Most air crashes are caused by multiple factors, with a preliminary report expected about 30 days after the accident.

Two of the GE recorders, one in the jet's front and another at the rear, are installed on Boeing's 787 jets and record the same set of flight data. GE, which sent experts to India, manufactured the engines on the Air India 787 and also produced the combined flight data and cockpit voice recorder, called an "enhanced airborne flight recorder".

The forward recorder is equipped with an independent power supply that provides backup power to the device for about 10 minutes if the plane's power source is lost, the NTSB said in a 2014 report.

The decision to begin downloading recorder data around two weeks after the crash was unusually late, three experts told Reuters, and followed speculation that the so-called black boxes could be sent to the United States for analysis.

U.S. aviation safety expert Anthony Brickhouse said accident investigators would typically have already given some update on the recorders' status, and have begun downloading data in such a high profile crash.

"Normally countries know that the world is watching," he said.

India said last week that it was yet to decide where the black boxes would be analysed. The data retrieved from them could provide critical clues into the aircraft's performance and any conversations between the pilots preceding the crash.

India has said its actions have been taken in full compliance with domestic laws and international obligations in a time bound manner.

(Reporting by Sakshi Dayal in New Delhi and Allison Lampert in Montreal; Editing by YP Rajesh and Philippa Fletcher)