In the past few months, deep in the forbidding deserts of central Syria, Russian forces have quietly joined the Syrian military in intensifying attacks against Islamic State strongholds, including bombing what local news reports called the dens and caves where the extremist fighters hide.
While the world was focused on the conflicts in Ukraine and Gaza, this type of skirmishing has been simmering for years in Syria, and the Islamic State has long threatened to strike Russia directly for shoring up the regime of its sworn enemy, President Bashar al-Assad of Syria.
That moment appeared to have come on Friday night with the bloody assault on a Moscow concert hall that left more than 130 people dead. “The fiercest in years,” said a statement of responsibility issued on Saturday by a branch of the Islamic State via its news agency, referring to the long history of brutal terrorist attacks pitting jihadist forces against Moscow.
“They have framed this attack as coming in the context of the normal, ongoing war between ISIS and the anti-Islamic countries,” said Hanna Notte, a Berlin-based expert on Russian foreign and security policy at the James Martin Center for Nonproliferation Studies. “This seems to be within the overarching theme of Russia in Afghanistan, Russia in Chechnya, Russia in Syria.”
In his brief remarks on Saturday, President Vladimir V. Putin of Russia did not mention the claim from the Islamic State, but he did threaten to punish those responsible. “All perpetrators, organizers and commissioners of this crime will receive a just and inevitable punishment,” Mr. Putin said.
The Russian president spoke with Mr. al-Assad about counterterrorism cooperation, among other issues, in a phone call on Saturday, the Kremlin said.
Russian state television, dismissing responsibility claims by ISIS, instead suggested that it was a “false flag” operation by Ukraine, possibly with Western backing. The White House issued a statement on Saturday repeating the U.S. assertion that ISIS was responsible.
Russia has unquestionably been in the cross hairs of jihadist organizations for a while. The animosity first welled up during the decade-long Soviet war in Afghanistan, continued through during Russia’s two brutal wars in Chechnya and escalated when the Russian Air Force was deployed to Syria in September 2015.
That October, a group of 55 Saudi clerics issued a statement calling for what they described as a holy war against Russia as punishment for its military intervention in Syria and predicted that Russia would suffer a defeat similar to that in Afghanistan.
Late that October, an Islamic State affiliate in Egypt claimed responsibility for planting a bomb on a charter flight carrying tourists back to St. Petersburg, Russia. The explosion over the Sinai Peninsula killed all 224 people aboard. Shortly after the attack, Dmitri S. Peskov, Mr. Putin’s spokesman, rejected any link between that episode and Russia deploying its forces to Syria.
The Islamic State’s propaganda wing soon released a video of a chant in Russian that included the chorus, “Soon, very soon, blood will spill like the sea.” The lyrics of the song also suggested that Muslim rule would return to Russian regions where about 20 million Muslims form a substantial part of the population, including the Caucasus, Tatarstan and in annexed Crimea.
Russia was keenly aware of the threat. A spate of bloody attacks carried out mostly by homegrown extremists against a school, a Moscow theater, transportation hubs and other targets left hundreds of Russians dead in the 2000s.
The Kremlin, hoping that no terrorist incident would mar the 2014 Winter Olympics, gave what was considered at least tacit approval for extremists from the Caucasus or from among the Central Asian immigrant communities in Russia to depart. Thousands left. Russian became the second most prevalent language among Islamic State fighters after Arabic, said Colin P. Clarke, a counterterrorism expert with The Soufan Center.
In February 2017, Mr. Putin said that about 4,000 Russians and another 5,000 people from Central Asian countries that were part of the Soviet Union had gone to fight in Syria. “We understand what a huge danger lies in this hotbed of terrorism on the territory of Syria for us, for Russia,” he said during meeting with military personnel.
In looking at the videos from the Russian concert hall attack, Mr. Clarke said that the four attackers seemed well coordinated. He said he suspected that they had trained at an Islamic State camp in Afghanistan and were dispatched to Russia.
“This was not an attack by some radicalized guys acting on their own,” Mr. Clarke said. “This was not their first rodeo — the way they shot, the way they spaced out from each other, the way they moved.”
Although the Islamic State has lost its caliphate in Syria and Iraq, that did not destroy the idea or the cause, said Andrew J. Tabler, a former U.S. government official on security issues in the Middle East and a senior fellow specializing in Syria at the Washington Institute for Near East Policy.
Though diminished, the Islamic State, sometimes known as the Islamic State of Iraq and Syria, or ISIS, retains global reach with its different branches. European security agencies said they had thwarted planned attacks in recent years, including one in April 2020, when Germany said that it had foiled a plot by adherents to Islamic State Khorasan Province, or ISIS-K, in a Tajik immigrant community to attack NATO bases.
The wing that took responsibility for the Moscow attack on Friday is known as ISIS-K. The group emerged among opponents of the Taliban in Afghanistan — the K stands for the region of Khorasan, which includes parts of what is now Afghanistan, Pakistan, Iran and Turkmenistan.
On March 7, the Federal Security Service, Russia’s main law enforcement agency, said that it had prevented an attack planned by the Islamic State against a Moscow synagogue. The State Department said in a statement Saturday that at the same time the United States had shared an intelligence report with Russia about a possible attack on a concert venue.
“What happens in Syria doesn’t stay in Syria, never has for the whole war,” Mr. Tabler said. “I think that this is payback for the Russians intervening on behalf of the Assad regime.”
Analysts noted that neither jihadist organizations nor ordinary Syrians had forgotten that the Russian Air Force has hit hospitals and other civilian targets, or that Russian cruise missiles have slammed into Syrian cities.
Not long after the Russian invasion of Ukraine, the main propaganda arm of the Islamic State spotlighted the war in its al-Naba newsletter, with a headline reading: “Crusader Against Crusader Wars.”
The group celebrated the idea that two Christian powers in Europe were locked in a mutually destructive war, noted Mr. Clarke in an article for Foreign Policy. “This bloody war taking place today, between the Orthodox crusaders — Russia and Ukraine — is an example of the punishment that was unleashed upon them and is forever glued to them,” the ISIS article said.
When it comes to the Islamic State, it appears equally hostile to Russia, the United States and Iran, Mr. Clarke said in an interview. “It is just different flavors of apostate for them.”
Hwaida Saad and Milana Mazaeva contributed reporting.