A search for bodies is taking place after a Russian military plane carrying 92 people crashed in the Black Sea.
The Russian intelligence agency has said it sees no signs of a possible terror attack in Sunday's Black Sea plane crash.
The FSB agency said it "has not found any signs or facts pointing to a possible terror attack or sabotage on board" and is focusing on possibilities including pilot error, low quality of fuel, external objects getting in the engine or an unspecified technical fault.
The plane was heading to Syria when it came down yesterday.
The passengers included dozens of singers in Russia's world-famous military choir the Alexandrov Ensemble, nine Russian journalists and a Russian doctor known for her charity work in war zones.
A national day of mourning is taking place in Russia.
Soloist Vadim Ananyev had got permission to skip the concert to help his wife as they just had a new baby.
Mr Ananyev said: "I have lost my friends and colleagues, all killed, all five soloists - I feel in complete disarray."
He said: "It is such a shame. I have known these people for 30 years. I know their wives and children. I feel terrible for the children and for all that I have lost."
Mr Ananyev said he has received condolences from all over Russia and from abroad.
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.