The Russian passenger plane which crashed in Egypt in October was the result of a "terrorist" act, the head of Russia's FSB security service has said.
Alexander Bortnikov told President Vladimir Putin on Tuesday that a home-made explosive device blew up on the Airbus.
All 224 people on board the Metrojet plane, most of them Russian tourists, were killed in the October 31 crash in the Sinai Peninsula.
Mr Bortnikov said: "According to our experts, a home-made explosive device equivalent to 1kg of TNT went off on board, which caused the plane to break up in the air, which explains why the fuselage was scattered over such a large territory. I can certainly say that this was a terrorist act."
Mr Putin vowed to hunt down those responsible for the attack.
"There's no statute of limitations for this, we need to know all of their names," the president said. "We're going to look for them everywhere, wherever they are hiding. We will find them in any place on Earth and punish them."
Islamic State (IS) has claimed responsibility for bringing the Russian plane down in written statements, as well as video and audio messages posted on the internet following the crash.
It said the attack was in retaliation for Russia's air campaign against IS - and other groups - in Syria, where Moscow wants to preserve the rule of President Bashar Assad.
The group warned Mr Putin that it would also target him "at home" but did not offer any details to back its claim.
While releasing specifics would add credibility, the group may be withholding either because its claim is false, or because doing so would undermine plans for similar attacks in the future - or because the aura of mystery might deepen its mystique among die-hard followers.
IS has also claimed responsibility for the attacks in Paris last Friday which killed 129 people and wounded 350 others.
US prosecutors have unveiled criminal charges against three men accused of running a sprawling computer hacking and fraud scheme that included a huge attack against JPMorgan Chase and generated hundreds of millions of dollars of illegal profit.