"All possible versions are being looked into and it's too early to say anything with certainty, but as you know, the version of an act of terror is by far not at the forefront," Peskov told journalists.

Thousands of rescuers were searching for bodies in the Black Sea as Russia marked a day of mourning Monday following the crash of a Syria-bound military plane.

The Tu-154 jet, whose passengers included more than 60 members of the internationally-renowned Red Army Choir who were heading to entertain Russian troops in Syria for the New Year, went down off the resort city of Sochi shortly after take-off Sunday.