The A321 plane crash was caused by the blast of an improvised explosive device, Federal Security Service Director Alexander Bortnikov said at a conference chaired by the president.

"An improvised explosive device equivalent up to 1 kilograms of TNT went off during the flight. As a result, the plane disintegrated in midair, which explains widely scattered fuselage pieces," Bortnikov said.

An A321 plane of the Kogalymavia airline carrying 217 passengers and seven crewmembers en route from Sharm el-Sheikh to St. Petersburg crashed on October 31 on the Sinai Peninsula.