Several assailants burst into a large concert hall in Moscow on Friday and sprayed the crowd with gunfire, killing at least 40 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, which couldn’t be independently verified. It wasn’t immediately clear what happened to the attackers after the raid, which Moscow Mayor Sergei Sobyanin described as a “huge tragedy” and state authorities 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.