No survivors have been spotted after a military plane carrying 92 people, including a well-known military band, crashed near Sochi, Russia's defence ministry has said.
A total of 84 passengers and eight crew members were on the Tu-154 plane when it disappeared from radar two minutes after taking off in good weather.
Emergency crews found fragments of the plane about 1.5 kilometers (less than one mile) from shore. By Sunday afternoon, rescue teams had already recovered 10 bodies from the crash site.
The plane was carrying Russian servicemen and 64 members of the Alexandrov Ensemble, among them its leader Valery Khalilov, who were being flown into Russia's Hmeymim air base in Syria to entertain military personnel in the run-up to the new year.
Also on board was Yelizaveta Glinka, a Russian doctor who has won wide acclaim for her charity work. Her foundation said that Glinka was accompanying a shipment of medicines for a hospital in Syria.
Nine Russian journalists from three Russian television stations were also among the passengers.
More than 3,000 people — including dozens of divers — worked from 27 ships and several helicopters to search the undersea crash site, according to the Defense Ministry.
Drones were also flown over to help spot bodies and debris. Around 100 more divers were being flown in from naval facilities across Russia, and officials brought in powerful spotlights so the search could continue around the clock.
Russian Defense Ministry spokesman Major General Igor Konashenkov said 10 bodies had been recovered so far "No survivors are seen," he added.
An unnamed ministry source told Russian news agencies no life rafts had been found, while another source told the Interfax agency that the plane had not sent an SOS signal.
Viktor Ozerov, head of the defence affairs committee at the upper house of Russian parliament, said the crash could have been caused by a technical malfunction or a crew error, but he believes it could not have been terrorism because the plane was operated by the military.
"I totally exclude" the idea of an attack bringing down the plane, he said in remarks carried by state RIA Novosti news agency.
However, some experts contested Mr Ozerov's claim, saying the crew's failure to report a malfunction pointed to a possible terror attack.
"Possible malfunctions ... certainly wouldn't have prevented the crew from reporting them," Vitaly Andreyev, a former senior Russian air traffic controller, told RIA Novosti, adding that it points at an "external impact."
Speaking in St Petersburg, Russian President Vladimir Putin declared 26 December a national day of mourning.
He said the government will "conduct a thorough investigation into the reasons and do everything to support the victims' families."
Russia's Defence Ministry regularly flies musicians into Syria to put on concerts for military personnel. The base they were heading for, Hmeymim, is in Latakia province, from where Russia conducts air strikes against Syrian rebels.
Syrian President Bashar al Assad told Russia he was saddened by the crash.
In a condolence message sent to Mr Putin, Mr Assad said the two countries were partners in the "fight to lay the foundations of stability, security and peace" in Syria.
"Our prayers are with you ... our sorrows and joys are one," Mr Assad said. "The plane had dear friends who had come to join us and the people of Aleppo in their joy with victory and Christmas feasts."
In April 2010, a Tu-154 carrying Polish President Lech Kaczynski and 95 others crashed while trying to land at a sporadically used military airport in Smolensk in western Russia, killing everyone on board.
Investigations by both Polish and Russian experts blamed pilot error in bad weather conditions, but Polish authorities have launched a new probe.
Additional reporting by agencies
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