SOCHI, Russia -- A pilot error or a technical fault -- not terrorism -- is likely to be the cause of the plane crash into the Black Sea, Russia's transport minister said Monday 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 Sunday morning when it crashed two minutes after taking off from the southern Russian city of Sochi. 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.
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 Defense Ministry said. Helicopters, drones and submersibles were being used to help spot bodies and debris. Powerful spotlights allowed the operation to go on all through the night.
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.
The plane was taking the Defense 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.
The plane originated from Moscow's military airport of Chkalovsky and stopped in Sochi for refueling before heading to Syria. Despite the Syrian connection, Sokolov said the government sees no need to heighten security measures at Russian airports.
Emergency crews on Sunday found fragments of the plane about a mile from shore, but a deputy defense minister told Russian news agencies that experts estimated the Tu-154 crash site at 3.7 miles from shore.
By Monday morning, rescue teams had recovered 11 bodies as well as fragments of bodies. Those were flown to Moscow, where the remains will be identified.
Russian President Vladimir Putin went on television to declare Monday a nationwide day of mourning.
Some choir members did not go to Syria for personal reasons. Soloist Vadim Ananyev stayed behind to help his wife with the kids as they just had a new baby.
"I have lost my friends and colleagues, all killed, all five soloists - I feel in complete disarray," Ananyev told The Associated Press. "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."
Ananyev said he had received condolences from all over Russia and from abroad.
"We were loved all over the world, never mind the political situation," he said.
Mourners stopped by the Sochi Adler airport on Monday to light candles at the airport's chapel and lay flowers at an improvised shrine that featured photos of the plane and of some victims.
The Tu-154 is a Soviet-built three-engine airliner designed in the late 1960s. More than 1,000 have been built, and they have been used extensively in Russia and worldwide. The plane that crashed Sunday was built in 1983, and underwent factory check-ups and maintenance in 2014, the Defense Ministry said.
The Black Sea search area -- which covers more than four square miles -- is plagued by underwater currents that can carry debris and body fragments into the open sea. 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 over four miles east of the Sochi airport, to help monitor the Black Sea area for possible plane fragments or bodies.
Despite the transport minister's comments downplaying the possibility of a terror attack, Russian planes have been hit before by attacks, including one just last year.
In October 2015, a plane carrying mostly Russian tourists back from vacation in Egypt was brought down by a bomb over the Sinai Peninsula, killing all 224 people aboard. The local affiliate of the Islamic State group claimed responsibility.
Kate de Pury contributed to this report from Moscow.
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