Several camouflage-clad gunmen opened fire at a popular concert venue on the outskirts of Moscow on Friday (Mar 22) night, killing at least 40 people and wounding more than 100, Russia’s top security agency said, which would make it the deadliest attack in the capital region in years.

A branch of the Islamic State group claimed responsibility, and US officials confirmed the claim shortly afterward. The United States collected intelligence in March that the Islamic State group’s Afghanistan affiliate had been planning an attack on Moscow, according to officials.

As gunshots boomed through the building containing the concert hall, one of the largest and most popular music venues in the Moscow area, fire erupted in the upper floors of the structure, and the blaze intensified after an explosion, news agency RIA Novosti reported.

Multiple videos posted on social media and verified by The New York Times show several people entering the venue – Crocus City Hall, a sprawling shopping and entertainment complex in suburban Krasnogorsk, northwest of Moscow – and firing rifles. Other videos show people running past bloodied victims lying on the floor or screaming at the sound of gunshots, while photos show bodies lined up outside the building.

The shooting occurred minutes before a sold-out performance by veteran rock band Piknik was scheduled to start. The concert hall has 6,200 seats, according to its website.

A woman who gave her name only as Marina said in a text message that she was standing in line for the concert outside, in the cold, about 8 pm when people without overcoats started running out of the building, saying they had heard shots.

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“As soon as I heard automatic rifle shots I started running, too,” she said.

State news agency TASS reported that emergency services had dispatched helicopters to try to rescue people from the building’s roof, where flames and smoke could be seen billowing into the night sky. The roof near the concert stage was collapsing around 10 pm, RIA Novosti reported.

Russia’s Investigative Committee, the country’s equivalent to the FBI, said it had opened a criminal case into a terrorist act and dispatched its investigators to the site. RIA Novosti said a special police unit was working inside the building.

Mykhailo Podolyak, a top adviser to Ukraine’s presidential office, said in a video statement that “Ukraine has absolutely nothing to do” with the attack. John Kirby, a spokesperson for US President Joe Biden’s National Security Council, told reporters that the White House had “no indication at this time that Ukraine or Ukrainians were involved.”

The attack appeared to be one of the deadliest in Russia in decades. The deadliest was the Beslan school siege of 2004, when more than 330 people were killed as Chechen militants, who took more than 1,000 people hostage, battled Russian forces in a school in southern Russia. Two years earlier, militants seized a crowded Moscow theater in 2002; more than 100 hostages died in that standoff, after Russian special forces pumped an aerosol version of fentanyl into the theater in an attempt to incapacitate the gunmen. NYT