The jet with some 91 people onboard, including 83 passengers and eight crew members lost contact with land while flying over the Black Sea, the source said.
Journalists, military personnel, musicians from Alexandrov Ensemble, an official army choir of the Russian armed forces, were onboard. Initially it was reported that the plane was carrying some 70 people.
"According to preliminary findings, the missing TU-154 arrived in Sochi from Chkalovsky airport in Moscow region for refueling. Most likely, it crashed in mountainous area of Krasnodar Territory," the source told RIA Novosti.
The priliminary data shows that the disappeared plane was heading to Syria's Hmeimim airbase. According to the source, the possible reasons for the alleged crash could be technical malfunction or pilot error.
The source added that the plane disappeared from radars 20 minutes after departing from Sochi, Krasnodar Krai.
SPUTNIK/MNA