Debris and 11 bodies have been found after a Russian military plane with 92 people on board crashed into the Black Sea.
The plane disappeared from radar two minutes after taking off from Sochi at 5.25am local time on Christmas Day, heading for Latakia in Syria.
There are no survivors from the crash, the Russian defence ministry said.
A defence ministry spokesman, Maj-Gen Igor Konashenkov, said more than 100 divers had been inspecting the seabed in an operation continuing through the night.
The Tu-154 was carrying soldiers, reporters and 64 members of the famed Alexandrov military music ensemble who were to perform for Russian troops.
Russia's transport minister said investigators were looking into an "entire spectrum'' of possible reasons the crash occurred, including the possibility of a terror attack.
Earlier, a Russian official had downplayed any suggestion of a terror attack.
President Vladimir Putin said Monday would be a day of national mourning.
The flight had originated in Moscow and landed at Adler airport in Sochi for refuelling.
The defence ministry said in a statement: "Fragments of the Tu-154 plane of the Russian defence ministry were found 1.5km from the Black Sea coast of the city of Sochi at a depth of 50 to 70m (165-230ft)."
Gen Konashenkov said: "No survivors have been spotted."
An audio recording played on Russian media and said to be of the final conversation between air traffic controllers and the plane revealed no sign of any difficulties being faced by the crew.
Voices remain calm until the plane disappears and the controllers try in vain to re-establish contact.
Reports from the area said flying conditions were favourable.
Gen Konashenkov said the plane was last serviced in September and had undergone more substantial repairs in December 2014. It had an "experienced" pilot.
President Putin has ordered a state commission to look into the crash and sent his condolences to the families and friends of the victims.