The death toll in Friday’s terror attack on a concert in Moscow has risen to at least 115, with authorities saying they have apprehended 11 suspects, four of whom were directly involved in the onslaught.

The Islamic State of Iraq and Syria (ISIS) claimed responsibility for the deadly attack in a statement on its affiliated social media channels, and the U.S. has said it has intelligence confirming that, according to several outlets. Russia’s Investigative Committee said it has opened a criminal probe into the attack.

The surprise attack began when gunmen donning combat gear burst into Crocus City Hall in the city of Krasnogorsk, where concertgoers were gathering to hear the Russian band Picnic. Video online showed gunmen opening fire, shooting attendees at close range and setting off smoke bombs. 

 A view of damage at Crocus City Hall concert venue near Moscow, Russia after fire was extinguished following a gunman’s attack that claimed the lives of at least 115 people. (Sefa Karacan/Anadolu via Getty Images)

RUSSIA INVESTIGATING SHOOTING, EXPLOSIONS AT CONCERT HALL AS TERRORIST ATTACK

The gunmen also threw explosives inside the concert hall during the attack, rocking the building and setting it on fire, Russian media reported. People were being evacuated, but some remained trapped inside the burning building, Russian media said. 

The roof of the theater collapsed in the early hours of Saturday morning as firefighters spent hours fighting the flames. Russians laid flowers at memorials and lined up to give blood.

«Intelligence agencies have detained 11 people, including four terrorists, who were directly involved in an attack on the Crocus City Hall, Russia’s Federal Security Service (FSB) said in a statement, according to Russian state news agency Tass.

«It has already been established that the terrorist attack was carefully planned. The weapons that the terrorists used had been placed in a cache in advance,» the FSB noted.

The FSB had been pinning the blame on Ukraine, with Russia’s Investigative Committee saying that four suspects were stopped in the Bryansk region of western Russia, «not far from the border with Ukraine.» 

RUSSIA INVESTIGATING SHOOTING, EXPLOSIONS AT CONCERT HALL AS TERROR ATTACK

They planned to cross the border into Ukraine and «had contacts» there, state news agency Tass said, citing Russia’s FSB. 

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.» 

The attack came just days after Russian President Vladimir Putin cemented his grip on power in another electoral landslide. The attack was the deadliest in Russia in years and came as the country’s fight in Ukraine dragged into a third year.

A massive blaze is seen over the Crocus City Hall on the western edge of Moscow, Russia, on March 22, 2024. Several gunmen have burst into a big concert hall in Moscow and fired automatic weapons at the crowd.

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Putin has wished all those injured a speedy recovery and praised medical staff, Deputy Prime Minister Tatyana Golikova said.

«We together with [Russian Health Minister] Mikhail A. [Murashko] reported to the president on the state of health of patients, the president wished all a recovery and conveyed compliments to doctors,» she told reporters.

Russian special services are still conducting search operations. Moscow Mayor Sergey Sobyanin canceled all mass events in the capital in the next two days, and a number of other Russian regions followed suit.

Fox News’ Brie Stimson and The Associated Press contributed to this report.