More than 60 people have been killed and 145 others were injured after assailants opened fire at a large concert hall in Moscow before setting fire to the venue.

The attack on the Crocus City Hall, a large music venue on Moscow’s western edge, comes just days after President Vladimir Putin cemented his grip on power in a highly orchestrated electoral landslide.

The so-called Islamic State group (IS) claimed responsibility for the attack in a statement posted on affiliated channels on social media.

A US intelligence official told The Associated Press that American agencies had learned the group’s branch in Afghanistan was planning an attack in Moscow and had shared the information with Russian officials.

It is not immediately clear what happened to the attackers after the raid, which state investigators are treating 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 Mr Putin was informed minutes after the assailants burst into the 6,200-capacity music venue.

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 that more than 60 people were killed. Health authorities released a list of 145 injured, 115 of whom were taken to hospital, 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 fire engines, 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.

Guards at the concert hall did not have guns, and some could have been killed at the start of the attack, Russian media reported.

Some Russian news outlets suggested the assailants fled before special forces and riot police arrived.

Reports said police patrols were looking for several vehicles the attackers could have used to escape.

In a statement posted by its Aamaq news agency, IS said it attacked a large gathering of “Christians” in Krasnogorsk on Moscow’s outskirts, killing and wounding hundreds. It was not immediately possible to verify the authenticity of the claim.

However, US intelligence officials confirmed the claim by the IS group’s branch based in Afghanistan that it was responsible for the Moscow attack.

Noting that the IS statement cast its claim as an attack targeting Christians, Aymenn Jawad al-Tamimi, an expert on the terrorist group, said it appeared to reflect the group’s strategy of striking wherever they can as part of a global attempts to “fight the infidels and apostates everywhere”.

On March 7, Russia’s top security agency said it thwarted an attack on a synagogue in Moscow by an IS cell, killing several of its members in the Kaluga region near the Russian capital. A few days earlier, Russian authorities said six alleged IS members were killed in a shootout in Ingushetia in Russia’s Caucasus region.

Russian officials said security was tightened at Moscow’s airports, railway stations and the capital’s sprawling subway system. Moscow’s mayor cancelled all mass gatherings, and theatres and museums shut for the weekend. Other Russian regions also tightened security.

The Kremlin did not immediately blame anyone for the attack, but some Russian legislators were quick to accuse Ukraine and called for ramping up strikes.

Dmitry Medvedev, deputy head of Russia’s Security Council, said that if Ukraine involvement was proven, all those involved “must be tracked down and killed without mercy, including officials of the state that committed such outrage”.

However, Mykhailo Podolyak, an adviser to Ukrainian President Volodymyr Zelensky, denied Ukraine involvement.

“Ukraine has never resorted to the use of terrorist methods,” he posted on X. “Everything in this war will be decided only on the battlefield.”