Here's what we know about the deadly Russian plane crash that killed all 224 people on board Saturday, Oct. 31. (Monica Akhtar/The Washington Post)

Russian officials on Tuesday confirmed that the midair explosion of a Russian jetliner over the Sinai desert last month that killed all 224 people aboard was the result of a terrorist attack.

In response, Russia significantly stepped up its airstrike campaign in Syria, deploying long-range bombers from Russian soil to strike targets there, and President Vladimir Putin on Tuesday vowed that the culprits behind the bombing of the plane would be “found and punished.”

Putin also called for greater military collaboration in Syria with French forces launching airstrikes against the Islamic State. Putin and French President François Hollande are set to meet next week following a spate of recent terrorist attacks, including Friday’s in France that left 129 dead.

At a meeting with Putin, Federal Security Service head Alexander Bortnikov said traces of explosives found in the plane’s wreckage indicated that an improvised explosive device was detonated onboard.

The statement marked the first time Russian authorities have verified that the crash was the work of terrorists. Western leaders, including President Obama and British Prime Minister David Cameron, said just days after the Oct. 31 tragedy that a bomb may have been responsible.

An affiliate of the Islamic State claimed responsibility for the plane crash in the days following the attack, although the claim could not immediately be verified.

“We can say conclusively that this was a terrorist act,” Bortnikov said Tuesday, according to an official transcript of the briefing.

Meanwhile, in Egypt, authorities Tuesday detained two employees of Sharm el-Sheikh airport in connection with the downing of the Russian jet, two security officials told the Reuters news agency. The airliner was traveling from the Sinai resort city of Sharm el-Sheikh en route to St. Petersburg, when it exploded in midair and crashed into the desert.

“Seventeen people are being held,” said one of the officials, according to Reuters. “Two of them are suspected of helping whoever planted the bomb on the plane at Sharm el-Sheikh airport.”

Egypt has not confirmed that a bomb was responsible, saying it wants to wait until all investigations are complete.

Putin, flanked by Bortnikov and other top advisers in Moscow at a briefing of Russia’s National Anti-Terrorism Committee, said those behind the attack would be brought to justice.

“We will search for them everywhere, no matter where they are hiding,” he said in remarks that were later televised. “We will find them at any point on the planet and punish them.”

The Russian government offered $50 million Tuesday for information about those behind the attack. Neither Bortnikov nor Putin mentioned the Islamic State by name Tuesday, although Putin directed Russia’s military to intensify airstrikes in Syria, where the group’s strongholds are located.

Russia launched an intervention in Syria in late September to back the government of Syrian President Bashar al-Assad against its enemies, including the Islamic State and a hodgepodge of Islamist and more-moderate rebel forces. Dmitry Peskov, Putin’s press secretary, ruled out a ground operation in Syria when questioned about Putin’s statements Tuesday.

Putin also said that Russia would invoke its right to self­defense under the U.N. charter and called on other countries to aid Russia in its search for the culprits.

“Anyone who tries to supply help to the criminals should know that the consequences for trying to harbor them will lie squarely on their shoulders,” he said.

The Russian government suspended flights to Egypt on Nov. 6 because of concerns of lax security at the airport in Sharm el-Sheikh. The jet went down shortly after takeoff.

Russian tourism officials said this week that more than 70,000 tourists have returned from Egypt, Russia’s most popular tourist destination outside the former Soviet Union. They have been ferried back to Russia under tight security controls, including a ban on checked luggage, to prevent a bomb from being smuggled aboard.

Similar measures have been taken by a half-dozen European airlines.

Russian officials initially urged patience until the investigation concluded, but experts said that Tuesday’s news had probably been expected in the Russian government.

“This will not come as too much of a shock to the Russians,” said Dmitri Trenin, the head of the Carnegie Moscow Center.

Trenin said that he did not expect the public to blame Russia’s government for the crash, nor did he think the terrorist attack would sharply change Russia’s foreign policy.

“The Russians have been living in this atmosphere of potential terrorism for a long time, since the 1990s, nonstop virtually,” Trenin said. “It’s not the kind of revelation that the French have just experienced.”

In Moscow, many people said they believed the plane was brought down by an attack even before Tuesday’s confirmation.

“I was sure it was a terror act from the very beginning,” said Aleksey Kalganov, 37, an engineer dressed in a dark blue jacket, checked scarf and gray cap. “A plane cannot just fall apart in the air.”

Metrojet, the airline managing the Airbus A321-200, made a similar argument at a news conference shortly after the crash, drawing a swift warning from Russian officials to “abstain from premature statements.”

Kalganov said he had always been afraid of flying because of the possibility of a terrorist attack and preferred traveling by car or train, even over long distances.

“This is their response, and I think that there might be more,” he said, adding that he believed the attack was tied to Russia’s airstrike campaign in Syria. “But nevertheless I support the campaign. They are crazy there, and we should destroy them.”

Others opposed the airstrikes.

“This is terrible,” said Elena Lopatina, 44, a manager, when asked about the news of the terrorist attack. “But I am not surprised.”

“No, I do not support the airstrikes. I am against the operation in Syria,” she continued. “I don’t think we can stop now, but I wish we could.”

Daniela Deane in London contributed to this report.

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