A bomb planted by terrorists brought down a Russian airliner in Egypt last month, the head of Russia's FSB intelligence agency said on Tuesday, as President Vladimir Putin vowed to "punish" the terrorists responsible for killing all 224 people on board.

"One can unequivocally say that it was a terrorist act," the head of the FSB, Alexander Bortnikov, said after a meeting with President Vladimir Putin on Monday, but then first announced by the Kremlin on Tuesday. Based on expert analysis, he said, a "homemade explosive device equivalent to 1 kilogram of TNT" brought down the plane.

The Metrojet Airbus A321 came apart at 30,000 feet (10,000 meters) nearly 20 minutes after taking off from the Sinai resort of Sharm el-Sheikh on October 31.

Debris was spread out over a large area, which Bortnikov said could be explained by a bomb. Traces of an explosive device were found in debris and on the belongings of passengers, he said.

The "Islamic State" group claimed credit for the attack, which it said was in retaliation for Russian airstrikes in Syria.

Within days US and British intelligence said IS claims were "likely" and suggested a bomb could have been snuck into luggage, but Egyptian and Russian officials were initially hesitant to conclude a terror act brought down the plane.

On Tuesday, Egyptian officials still seemed to be unaware, saying they would look into the Russian findings.

'Vengeance is inevitable'

Putin, whose air force started bombing in Syria in late September, vowed to not be deterred by a terror attack he called "among the bloodiest crimes in terms of victims."

"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 in a meeting with security officials late on Monday.

"We will search for them anywhere they might hide. We will find them in any part of the world and punish them," he said.

Putin did not assign blame to any group as the country offered a $50 million (47 million euros) reward for information leading to the capture of those responsible.

Changing dynamics

The Russian assessment that a terror attack brought down its airliner comes days after IS carried out coordinated terror attacks in Paris, killing 129. That attack, alongside those in Beirut and Ankara, show the group's increasing sophistication and ability to strike outside its self-declared caliphate in Syria and Iraq.

The terror attacks have reinvigorated efforts for a coordinated global response to deal with IS and resolve the five-year-old conflict in Syria, even as countries with different objectives and tactics towards Syria make slow progress to narrow the political gap.

The attacks could even bring Russia and France - who have not seen eye-to-eye on Syria - closer together on IS and Syria policy. France has called fora grand coalition to defeat IS.

Putin has also called for a tougher stance against IS, and on Monday said the Paris attacks proved that it was "indispensible" for a united front against the terror group.

Russia is one of the main backers of Syrian President Bashar al-Assad and has been accused by the west of primarily targeting western and Gulf-backed rebels in Syria in an effort to bolster the regime. Russia says it is striking IS and other "terrorist" groups.

But on Tuesday, a French official told Reuters that Russia has increased airstrikes on IS' de-facto capital of Raqqa, "which is proof that they too are becoming conscious (of the threat from Islamic State)."

As Russia sent more than two dozen additional aircraft to Syria on Tuesday, Putin told top military officials that they should work with France "as allies."

France for its part has used the Paris attacks to escalate its air campaign against IS in Syria and Iraq, and in a move on Tuesday EU defense ministers approved a French call for military assistance. France is sending its Charles de Gaulle aircraft to the eastern Mediterranean.

French President Francois Hollande is scheduled to meet next week with US President Barack Obama in Washington and Putin in Moscow to discuss coordinated efforts to respond to the IS threat.

Speaking in Paris on Tuesday, US Secretary of State John Kerry said diplomatic talks in Vienna had made progress and the country could be "weeks away, conceivably, of a big transition."

Kerry said that if political progress moves forward there could be greater room for the US and Russia to cooperate and coordinate airstrikes on IS in Syria.

cw/jil (AFP, AP, dpa, Reuters)