MOSCOW: Russia's security chief told President Vladimir Putin that a plane carrying 224 people over Sinai was downed due to a “terror attack,” the Kremlin said on Tuesday.

“One can say unambiguously that it was a terror act,” the head of the FSB security agency, Alexander Bortnikov, told Putin in a meeting the day before.

Citing experts, he said the plane disintegrated in midair due to a bomb with the equivalent of a kilo of TNT.

Read: Russian plane black boxes point to 'attack'

Black box data from the Russian plane that crashed in Egypt indicated it was hit by a bomb, sources said.

Investigators of the Russian plane crash in Egypt were "90 per cent sure" the noise heard in the final second of a cockpit recording was an explosion caused by a bomb, a member of the investigation team said.

The indications and analysis so far of the sound on the black box indicated it was a bomb,” said the Egyptian investigation team member.

Also read: Russia, Egypt dismiss US, UK claims bomb brought down jet