FSB chief Alexander Bortnikov has confirmed to Russian president Vladimir Putin that an “act of terror” brought down a Russian A321 airliner in Egypt last month.
The Russian security chief said “traces of foreign explosives” were found amid debris from the Airbus plane.
A branch of so-called Islamic State said it downed the plane.
Nearly all of the 224 people killed were Russian.
In a transcript of the meeting released on the Kremlin website, Bortnikov said a bomb had been planted on board the Kogalymavia jet.
The device was thought to be the equivalent of up to one kilogramme of TNT.
The bomb shattered the plane mid-air on October 31st.
Russia has offered a $50m reward for information on the Sinai plane attackers.
Most of the A321 passengers were Russian tourists flying home from the Red Sea resort of Sharm el-Sheikh.