Vladimir Putin said Russia would intensify its air strikes on Islamist militants in Syria and launch a global manhunt after the Kremlin concluded that terrorists had placed a bomb on a Russian passenger jet which broke up over Egypt last month.

"We will find them anywhere on the planet and punish them," President Putin said of the plane bombers, in a somber Kremlin meeting which was broadcast on Tuesday.

Until now, Russia had played down assertions from Western countries that the crash, in which 224 people were killed on Oct. 31, was the work of terrorists, saying it was important to let the official investigation run its course.

But four days after Islamist gunmen and bombers killed at least 129 people in Paris, the Kremlin released footage showing Alexander Bortnikov, the head of Russia"s FSB security service, telling a late night meeting on Monday that traces of foreign-made explosive had been found on fragments of the downed plane and on passengers" personal belongings.

"According to an analysis by our specialists, a homemade bomb containing up to 1 kilogram of TNT detonated during the flight, causing the plane to break up in mid air, which explains why parts of the fuselage were spread over such a large distance," said Bortnikov.

"We can unequivocally say it was a terrorist act," he said.

The Airbus A321, operated by Metrojet, had been returning Russian holiday makers from Sharm al-Sheikh in Egypt to St Petersburg when it broke up over the Sinai Peninsula, killing all on board. A group affiliated with Islamic State claimed responsibility, but until Tuesday Russia had said terrorism was just one possible scenario.