Russian investigators looking into a military plane which crashed into the Black Sea believe it was caused by a fault with the aircraft's wing flaps, according to reports.

A black box was found in the wreckage of the plane, which had 92 people on board when it plunged into the sea on Sunday.

The device is the first flight data recorder to be recovered from the Tu-154 jet, which came down two minutes after taking off from Sochi airport.

It will be sent to Moscow for analysis, a defence ministry official told TASS news agency.

According to the Interfax news agency, a second black box has been found in the wreckage but not yet raised to the surface.


Image: The flight data recorder was placed in metal cooking pot

All 84 passengers and eight crew members were killed in the crash, including dozens of singers in Russia's world-famous military choir who were on their way to Syria to entertain troops.

Russia's federal security service said it had "no signs or facts" to suggest the crash was an act of terror.

An investigation is focusing on pilot error, a technical fault, bad fuel and a foreign object in the engine as four possible causes.

Russia has grounded all its Tu-154 jets until it is known what brought down the aircraft.

Search teams find fragments of crashed Russian plane

The Russian defence ministry said the plane that crashed was built in 1983 and underwent factory check-ups and maintenance in 2014.

Search and rescue teams have recovered 12 bodies and 156 body fragments, it added.

On Monday, rescue workers recovered the plane's fuselage and brought it to shore.

Fragments of the jet were found 27 metres underwater, including "two elements of the plane's control mechanism".

More than 3,000 people and 27 ships have been involved in the search operation.