Russia on Tuesday pounded Islamic State targets in Syria after confirming that a bomb attack brought down its passenger jet over Egypt last month, killing all 224 people on board.
President Vladimir Putin pledged to hunt down and "punish" those behind the attack but did not blame any specific group as he ordered an intensification of Moscow's campaign in Syria, vowing "vengeance".
Russia's security agency announced a $50-million (47 million-euro) reward for information leading to the capture of those behind the attack but Egypt said investigators had yet to reach their conclusion about what brought down the Airbus jet.
Cairo said that it was enhancing security in airports around the country over the possibility that the Russian plane that crashed in the Sinai peninsula shortly after leaving Sharm el-Sheikh resort on October 31 might have been destroyed by a bomb.
"It is not the first time that Russia confronts barbaric terrorist crimes", Russian President Vladimir Putin said in a meeting with his security chiefs.
"The murder of our people in Sinai is among the bloodiest crimes in terms of victims," he said in comments released Tuesday, vowing to hunt down those responsible.
"We will search for them anywhere they might hide. We will find them in any part of the world and punish them," he said.
Moscow's confirmation of the attack -- the deadliest against a Russian target since the Beslan school massacre by Islamist rebels from the North Caucasus in 2004 -- comes days after a chain of attacks claimed by the Islamic State group killed at least 129 people in Paris.
Putin and French leader Francois Hollande agreed in a phone call to "ensure closer contact and coordination" on Syria between their armies and security services, the Kremlin said, as the Russian strongman ordered his navy to work with French forces in the Mediterranean "as allies".
Russia is backing forces loyal to President Bashar Al-Assad in the fight against what it says are IS and other "terrorist" groups while France is part of a separate US-led coalition targeting IS.
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- 'Homemade' bomb -
Russia's security chief Alexander Bortnikov told Putin that traces of explosives of "foreign production" had been found on the plane wreckage and that the jet carrying tourists back from Egypt was brought by a home-made 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.
The FSB later said it would pay "$50 million for information helping to arrest the criminals" and Russia's foreign ministry announced it was asking its "overseas partners" to help track down the perpetrators.
A group linked to IS had earlier claimed responsibility for downing the plane, and Russia had halted all flights to Egypt while refusing to initially endorse growing suspicions in Britain and the United States that the plane was blown up.
An Egyptian-led probe has yet to confirm the bombing but the country's interior ministry said it was stepping up airport security across Egypt given "the possibility that it was targeted by a terrorist attack."
Putin did not expressly blame IS for the attack on the passenger jet but pledged to ramp up air strikes in Syria, "so that the criminals understand that vengeance is inevitable."
Moscow on Tuesday for the first time sent its powerful long-range bombers to strike IS targets in the provinces around the jihadist strongholds of Raqa and Deir Ezzor and to fire cruise missiles at Idlib and Aleppo regions.
Defence Minister Sergei Shoigu said 206 "terrorist" targets had been hit in the latest wave of strikes.
France has also ratcheted up its strikes against IS targets around Raqa since the bloody attacks in Paris. Hollande will meet next week with Obama and Putin, as part of broad diplomatic push to end the war in Syria.
Putin has called for a united coalition against IS in Syria and on Monday reiterated that the attacks in France showed it was "indispensable" to join forces against the jihadists.