Russia concluded Tuesday that a bomb brought down one of its passenger jets over the Sinai Peninsula last month, with President Vladimir Putin vowing vengeance against those who carried out the attack.
"We will search for them anywhere they might hide," Putin said. "We will find them in any part of the world and punish them."
The Russian leader did not specifically blame the Islamic State for downing the Metrojet A-321 aircraft, killing all 224 aboard, but within hours launched an aerial bombardment on Raqqa, the Islamic State's self-described capital in northern Syria.
France also bombed Raqqa in response to last week's deadly terrorist attacks in Paris, with the Islamic State taking credit for both the destruction of the Russian jet and the carnage in the French capital that has shocked the world.
The Kremlin said Putin and French President Francois Hollande agreed in a telephone call to "ensure closer contact and coordination" in their attacks on Islamic State targets. Putin ordered the Russian navy in the eastern Mediterranean to work "as allies" with the French navy, while adding 37 planes to the Russian strike force off the shores of Syria.
The United States said Russia carried out a "significant number" of airstrikes on Raqqa, possibly including sea-launched cruise missiles and long-range bombers. U.S. defense officials said their Russian counterparts informed them ahead of time of the bombardment as part of an agreement between the two countries as both carry out air missions in Syria.
Putin said, "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."
Since September, Russia has been conducting airstrikes in Syria in support of President Bashar al-Assad, while the United States and its allies for more than a year have been conducting raids against Islamic State targets in Iraq and Syria.
The head of Russia's security service, Alexander Bortnikov, described the October 31 Metrojet crash as a terrorist act and that explosives were found in both the wreckage and on luggage from the aircraft.
"According to our experts, a homemade explosive device equivalent to one kilogram 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," Bortnikov said.
The Federal Security Service also announced a $50 million reward for information leading to the arrest of those responsible.
The Metrojet flight from the Egyptian resort of Sharm el-Sheikh was headed to St. Petersburg when it crashed in the northern part of the Sinai Peninsula.
Militants claiming links to the Islamic State group said they carried out the attack, and a number of foreign governments had earlier expressed their belief that it involved an explosive device, a contention Russian and Egyptian officials at first claimed was speculative.
Russia now has banned all commercial flights to and from Egypt. Officials in Egypt have shifted their focus away from the cause of the crash to speculation on what they consider a Western conspiracy against their country and the severe impact the crash is having on its key tourism industry.
Despite the Russian announcement about the cause of the crash in the Sinai, Egyptian officials said they have yet to reach a conclusion.
VOA Pentagon correspondent Carla Babb contributed to this report