Russia's President Vladimir Putin has vowed vengeance after Moscow confirmed a bomb attack brought down a passenger jet over Egypt last month, killing all 224 people on board.
"It is not the first time that Russia confronts barbarous terrorist crimes," Russian President Vladimir Putin said in a meeting late on Monday with his security chiefs.
"The murder of our people in Sinai is among the bloodiest crimes in terms of victims. We will not wipe away the tears from our soul and hearts. This will stay with us forever, but will not stop us finding and punishing the criminals," he said in comments released on Tuesday.
"We will search for them anywhere they might hide. We will find them in any part of the world and punish them," he said, calling the attack "one of the bloodiest crimes".
Russia's security chief Alexander Bortnikov told Putin that the passenger jet was brought down over the Sinai peninsula by a bomb with a force equivalent to one kilo of TNT.
"We can say unequivocally that this was a terrorist attack," Federal Security Service (FSB) head Bortnikov said.
In response to the attack, Putin pledged to step up air strikes in Syria where Moscow is conducting a bombing campaign it says is targeting the Islamic State group and other "terrorist" groups.
"The combat work of our aviation in Syria must not only be continued. It must be intensified so that the criminals understand that vengeance is inevitable," Putin said.
A group linked to IS had earlier claimed responsibility for downing the plane but Russia had said it was waiting for the official results of an investigation into the tragedy.
Putin ordered Russia's foreign ministry to contact all Moscow's partners for assistance and said that it was counting on "our friends" to help find and punish those responsible for the plane attack.