Russian Defence Ministry said on Thursday the wreckage of the plane that crashed into the Black Sea on Christmas Day shows no signs of damage from an explosion or fire.
The Syria-bound Russian military plane Tu-154 went down on Sunday shortly after it took off from the Black Sea resort of Sochi, killing all 92 people on board, including 64 musicians from the Russian Red Army Choir.
Two black boxes have been recovered so far and the investigators who are analysing the voice records says there is no evidence of an explosion on board. They are hoping to establish the cause of the incident within the next 30 days.
"We hope to reach final conclusions no earlier than in 30 days," Sergei Bainetov, head of flight safety for the Russian air force told a briefing.
He also said that investigators have not ruled out that a terrorist attack was responsible for the crash, adding it was only one of the theories under consideration.
"But this isn't the only type of terrorist act ... It could have been any type of mechanical impact, so we don't rule out a terrorist act," Bainetov said.