Divers have recovered fragments of the Russian passenger jet that crashed into the Black Sea, killing all 92 people on board.

In a statement, Russia's emergency situations ministry said that divers found several fragments of the plane one mile away from the shore and 25 metres (82 feet) under the sea.

READ: Pilot error or technical fault likely cause of plane crash

It said some of the debris has been recovered, and the divers are going back into the water to search for more.

All 92 people onboard the Russian military's Tu-154 plane are believed to have died on when the jet crashed two minutes after taking off from the southern city of Sochi en route to Syria.

More than 3,500 rescue workers are involved in the operation to find the remains those on board and plane debris.

As Russia held a day of mourning for the victims, pilot error or a technical fault - not terrorism - was being held as the most likely cause of the crash.

The passengers included dozens of singers in Russia's world-famous military choir, nine Russian journalists and a Russian doctor known for her charity work in war zones.

The search party has not yet found the plane's black boxes, Emergency Situations Minister Vladimir Puchkov told Russian news agencies. Transport Minister Maxim Sokolov said earlier that the plane's flight recorders did not have radio beacons, so locating them on the seabed was going to be challenging.

Speaking on television Mr Sokolov said terrorism was not among the main theories for the crash cause, and that authorities were looking into a possible technical fault or a pilot error.

The intelligence agency FSB echoed his comments later, saying it "has not found any signs or facts pointing to a possible terror attack or sabotage on board".

The intelligence agency is now focusing the probe on possibilities such as a pilot error, low quality of fuel, external objects getting in the engine or an unspecified technical fault.

The plane began its flight from Moscow's military airport of Chkalovsky. The FSB insisted the plane was under its surveillance and that only two people, both FSB officers, got onboard when the jet landed in Sochi for refuelling. The plane did not carry any military or dual-use cargo, the FSB said.

She plane was taking the Defence Ministry's choir, the Alexandrov Ensemble, to perform at a New Year's concert at Hemeimeem air base in Syria's coastal province of Latakia. Despite the Syrian connection, Mr Sokolov said the government saw no need to heighten security measures at Russian airports.

Emergency crews found fragments of the plane about 1.5 kilometers from the shore on Sunday but a deputy defence minister told Russian news agencies that experts estimated the Tu-154 crash site at 6 kilometers from the shore.

Ministry of Emergency Situations employees prepare rescue boats at a pier just outside Sochi, Russia. Photo: Viktor Klyushin/AP

By Monday morning, rescue teams had recovered 11 bodies as well as body fragments. All were flown to Moscow, where the remains will be identified. Local governor Veniamin Kondratyev told Russian state television that most of the bodies could be still inside the fuselage.

Russia also asked the authorities of Georgia's breakaway republic of Abkhazia, which lies just 7 kilometers east of the Sochi airport, to help monitor the Black Sea for plane debris or bodies.