MOSCOW (AP) — Assailants burst into a large concert hall in Moscow on Friday and sprayed the crowd with gunfire, killing over 60 people, injuring more than 100 and setting fire to the venue in a brazen attack just days after President Vladimir Putin cemented his grip on power in a highly orchestrated electoral landslide.

The Islamic State group claimed responsibility for the attack in a statement posted on affiliated channels on social media. A U.S. intelligence official told The Associated Press that U.S. intelligence agencies had learned the group’s branch in Afghanistan was planning an attack in Moscow and shared the information with Russian officials.

It wasn’t immediately clear what happened to the attackers after the raid, which state investigators were investigating as terrorism.

The attack, which left the concert hall in flames with a collapsing roof, was the deadliest in Russia in years and came as the country’s war in Ukraine dragged into a third year. Moscow Mayor Sergei Sobyanin called the raid a “huge tragedy.”

The Kremlin said Putin was informed minutes after the assailants burst into Crocus City Hall, a large music venue on Moscow’s western edge that can accommodate 6,200 people.

The attack took place as crowds gathered for a performance by the Russian rock band Picnic. The Investigative Committee, the top state criminal investigation agency, reported early Saturday that more than 60 people were killed. Health authorities released a list of 145 injured — 115 of them hospitalized, including five children.

Some Russian news reports suggested more victims could have been trapped by the blaze that erupted after the assailants threw explosives.

Video showed the building on fire, with a huge cloud of smoke rising through the night sky. The street was lit up by the blinking blue lights of dozens of firetrucks, ambulances and other emergency vehicles, as fire helicopters buzzed overhead to dump water on the blaze that took hours to contain.

The prosecutor’s office said several men in combat fatigues entered the concert hall and fired on concertgoers.

Dave Primov, who was in the hall during the attack, described panic and chaos when the attack began.

“There were volleys of gunfire,” Primov told the AP. “We all got up and tried to move toward the aisles. People began to panic, started to run and collided with each other. Some fell down and others trampled on them.”

Videos posted by Russian media and on messaging app channels showed men toting assault rifles shooting screaming people at point-blank range. One video showed a man in the auditorium saying the assailants had set it on fire, as gunshots rang out incessantly.