LONDON -- Russian President Vladimir Putin's government says investigators found traces of explosives amid the wreckage of the Metrojet airliner that crashed down onto Egypt's Sinai Peninsula in pieces at the end of October, proving it was a "terrorist act."
U.S. and other Western officials have maintained for weeks that it was likely a bomb that blew the Russian plane apart about 25 minutes after it took off from the Egyptian resort town of Sharm el-Sheikh on Oct. 31.
"According to our experts, a homemade explosive device equivalent to 1 kilogram (about 1.6 pounds) of TNT went off onboard, 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," the head of Russia's Federal Security Service told the emergency meeting of the Russian Security Council.
FSS chief Alexander Bortnikov said Russia was offering a $50 million reward for information leading to those who might have been involved in the attack on the plane.
The attack -- claimed by ISIS and belived by intelligence officials to have been the group's work -- killed all 224 people on board.
President Putin vowed to find and hold accountable those responsible for the attack.
"Our military work in Syria must not only continue, it must be strengthened in such a way so that the terrorists will understand that retribution is inevitable," Putin said.
Putin's military unleashed a heavy aerial bombardment on opposition militants in Syria in September, but it has focused thus far on groups other than ISIS in an an apparent effort to shore-up Russia's ally, Syrian President Bashar Assad, whose forces had been losing ground quickly prior to Moscow's intervention.
Some of the Russian strikes have hit ISIS targets, and Tuesday morning saw a new barrage of cruise missiles, launched from Russian warships in the Mediterranean, hit ISIS' de-facto capital of Raqqa in northern Syria. A U.S. defense official confirmed the new strikes to CBS News.
Various media outlets reported Tuesday that Egypt was holding two members of the Sharm el-Sheikh airport ground crew in connection to the case, but Egypt's Civil Aviation Ministry flatly denied those reports. As did the Interior Ministry, which labeled them "completely and utterly devoid of truth."
The Russian declaration that it was a bomb attack on the Metrojet flight came as Paris was still reeling from the shock of a brazen attack by eight suspected ISIS militants in the French capital on Friday, which left 129 people dead.
ISIS claimed responsiblity for the attack, which involved three teams of gunmen armed with assault rifles and suicide bombs who targeted a sports stadium, a concert venue and a popular street full of bars and restuaruants, and French President Francois Hollande said it was an "act of war" by the group.
CBS News senior security contributor Michael Morell, a former deputy director of the CIA, said Monday the series of operations suggested "we're in a whole new world" when it comes to countering the terror group, as it had demonstrably "developed an attack capability in the West."
"They told us they would do it, and they've now done it in Western Europe. They told us that they will do it in the United States. They will eventually do that, unless they are degraded," said Morell.
France has dramatically stepped-up it's aerial bombardment of ISIS targets inside Syria since the attacks.
Of the eight suspected attackers in Paris, five of them were French nationals, at least four of whom were living in an impoverished neighborhood of the Belgian capital prior to the carnage.
The Brussels neighborhood of Molenbeek has been the focus of a number of police raids in the wake of the Paris attacks, and CBS News correspondent Allen Pizzey reported Tuesday that authorities in Belgium consider their worst nightmare; a place where drugs, explosives and automatic weapons are readily available.