ISIS has claimed responsibility for an attack at a large concert hall in the Moscow, Russia, area that left more than 60 people dead and nearly 150 injured on Friday. 

The attack began when gunmen donning combat gear burst into Crocus City Hall, where concertgoers were gathering to hear the Russian band Picnic, and opened fire. 

The gunmen also threw explosives inside the concert hall during the attack, which set the building on fire, Russian media reported.  

People were being evacuated, but some remained trapped inside the burning building, Russian media said. 

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The Islamic State made the claim on its affiliated social media channels, and the U.S. has said it has intelligence confirming that, according to several outlets. 

Before ISIS claimed responsibility, Russian officials said the incident was being investigated as a terrorist attack but didn't say who was responsible.

Russia's Investigative Committee said it has opened a criminal probe into the attack. 

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Moscow Mayor Sergei Sobyanin called the attack a "huge tragedy," while former Russian President and current Deputy Chair of the Security Council of the Russian Federation Dmitry Medvedev wrote on Telegram that if "Moscow finds the perpetrators of the attack were connected with the ‘Kiev regime’ then all [Ukrainians] should be found and destroyed…including state officials." 

The attack comes on the heels of Russian President Vladimir Putin's landslide reelection and amid the war in Ukraine, more than two years after Moscow invaded the country. 

Ukrainian President Volodymyr Zelenskyy denied any Ukrainian involvement before ISIS claimed responsibility. 

"Ukraine certainly has nothing to do with the shooting/explosions in the Crocus City Hall (Moscow Region, Russia). It makes no sense whatsoever," he said on social media, adding, in part, "there is not the slightest doubt that the events in the Moscow suburbs will contribute to a sharp increase in military propaganda, accelerated militarization, expanded mobilization, and, ultimately, the scaling up of the war. And also to justify manifest genocidal strikes against the civilian population of Ukraine." 

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Rebekah Koffler, a strategic military intelligence analyst and the author of "Putin’s Playbook," told Fox News Digital, "Putin has been briefed on the attack and he ‘gave all the necessary instructions’ to the law enforcement and security services, according to his press secretary Dmitriy Peskov. The Russians are treating it as a terrorist attack." 

Before ISIS had laid claim, Koffler said Russian officials were already blaming the attack on Ukraine. 

The Russian Culture Ministry has canceled all mass and entertainment events in the coming days in the area. 

Along with all sports, cultural and other mass events being canceled in Moscow this weekend, restrictive measures have been introduced in a number of regions, including Leningrad, Voronezh, Vologda and other regions, Koffler added. 

The Associated Press contributed to this report.