Pilot error or a technical fault is thought to be the cause of Sunday's Black Sea plane crash that killed 92 people, Russia's transport minister has said as the nation held a day of mourning for the victims.
All 84 passengers and eight crew members on the Russian military's Tu-154 plane are believed to have died on Sunday when it crashed two minutes after taking off from the southern Russian city of Sochi. Passengers included dozens of singers in Russia's famous military choir, nine Russian journalists and a Russian doctor known for her charity work in war zones.
More than 3,000 rescue workers on 32 ships - including over 100 divers flown in from across Russia - have been searching the crash site at sea and along the shore, the Defence Ministry said. Helicopters, drones and submersibles were being used to help spot bodies and debris.
Transport Minister Maxim Sokolov said in televised remarks on Monday that terrorism was not among the main theories, and that authorities were looking into a possible technical fault or a pilot error.
Still, several aviation experts noted factors that could suggest a terror attack, such as the crew's failure to report any malfunction and the fact that plane debris was scattered over a wide area.
"Possible malfunctions ... certainly wouldn't have prevented the crew from reporting them," Vitaly Andreyev, a former senior Russian air traffic controller, told RIA Novosti.
Emergency crews on Sunday found fragments of the plane about 1.5 kilometers (1 mile) from the shore but a deputy defence minister told Russian news agencies that experts estimated the Tu-154 crash site at 6 kilometers (3.7 miles) from the shore.
By Monday morning, rescue teams had recovered 11 bodies which were flown to Moscow, where the remains will be identified.
Mourners light candles at Sochi Adler airport's chapel and laid flowers at an improvised shrine that featured photos of the plane and of some victims.
The plane, which originated from Moscow's military airport of Chkalovsky and stopped in Sochi for refuelling, was taking the Defence Ministry's choir, the Alexandrov Ensemble, to perform at a New Year's concert at the Russian 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.
The Black Sea search area - which covers over 10 square kilometers (about 4 square miles) - is plagued by underwater currents that can carry debris and body fragments into the open sea. Mr Sokolov said the plane's flight recorders did not have radio beacons, so locating them on the seabed was going to be challenging.
Russia asked the authorities of Georgia's breakaway republic of Abkhazia, which borders Russia just 7 kilometers (4.3 miles) east of the Sochi airport, to help monitor the Black Sea area for possible plane fragments or bodies.
Russian planes have been hit before by terror attacks, including one just last year.
In October 2015, a plane carrying mostly Russian tourists back from holiday in Egypt was brought down by a bomb over the Sinai Peninsula, killing all 224 people aboard. Officials said the explosive was planted in the plane's luggage compartment. Islamic State claimed responsibility.