Russian President Vladimir Putin has vowed to punish those behind the “barbaric terrorist attack”, saying four gunmen trying to flee to Ukraine had been arrested.

Kyiv has strongly denied any connection, with Ukrainian President Volodymyr Zelensky accusing Putin of trying to shift the blame onto them.

“The whole country is in mourning with those who lost their loved ones in this inhumane tragedy,” public television channel Russia 24 said on Sunday morning.

Putin, in his only public remarks on the attack, did not refer to IS’s claims of responsibility.

At least 133 people were killed when camouflaged gunmen stormed the Crocus City Hall, in Moscow’s northern suburb of Krasnogorsk, and then set fire to the building on Friday evening.

– ‘Machine guns, knives, firebombs’ –

The Islamic State group on Saturday wrote on Telegram that the attack was “carried out by four IS fighters armed with machine guns, a pistol, knives and firebombs,” as part of “the raging war” with “countries fighting Islam”.

A video lasting about a minute and a half shot by the gunmen has been posted on social media accounts typically used by IS, according to the SITE intelligence group.

The video appears to have been filmed from the lobby of the concert venue and shows several individuals with blurred faces and garbled voices, firing assault rifles with inert bodies strewn on the floor and a fire starting in the background.

The attack was the deadliest in Russia since the Beslan school siege in 2004.

Russian officials expect the death toll to rise further, with 110 still in hospital.

Rescue workers were still pulling bodies from the burnt-out building on Sunday as the nation mourned.

The emergency ministry has so far named 29 of the victims, the blaze has complicated the process of identification.

The ministry on Sunday posted a video of heavy equipment arriving at the venue to dismantle damaged structures and clear debris.

– ‘Morally crushed’ –

On the streets of the capital on Sunday, there was shock and grief.

“It is a tragedy. I was morally crushed,” Ruslana Baranovskaya, 35, told AFP.

“People don’t smile … everybody feels the loss,” said 73-year-old Valentina Karenina, a pensioner, standing on a street off Red Square, next to the Kremlin in the centre of Moscow.

Museums, theatres and cinemas around the country closed, and billboards were replaced with memorial posters.

Mourners continued to stream to the concert hall in northwest Moscow to lay flowers as a tribute to the victims.

More than 5,000 people donated blood following the attack, officials said, with many standing in long queues outside clinics.

Putin on Saturday had vowed “retribution and oblivion” to the “terrorists, murderers and non-humans” who carried out the “barbaric, terrorist attack.”

Several of his allies have called for the country to lift a moratorium on the death penalty — demands that have sparked concern among Kremlin critics.

Russia says it has arrested 11 in connection with the attack, including all four assailants. It has not named the shooters but said they were all foreign nationals.

– Putin points to Ukraine –

Putin has pointed to a Ukraine connection and has not publicly addressed IS’s claim of responsibility in the 36 hours since the attack.

“They tried to escape and were travelling towards Ukraine, where, according to preliminary data, a window was prepared for them on the Ukrainian side to cross the state border,” Putin said of the four attackers in a televised address to the nation on Saturday — his only public comments so far.

Ukraine’s Zelensky, in his own evening address Saturday, dismissed the suggestion that Kyiv had been involved.

“Putin and the other scum are just trying to blame it on someone else,” he said.

In Moscow, some doubted his claims that Ukraine was involved.

“I’m not inclined to the version about Ukraine’s involvement … this (attack) is more like those committed by Islamist extremists,” said Vomik Aliyev, a 22-year-old Muslim who often went to the concert hall.

– Site search to continue –

Russia’s Investigative Committee said the death toll had reached 133 and the governor of the Moscow region said rescuers would continue to scour the site for “several days.”

Health authorities said Sunday that 110 people were still in hospital, with more than 40 in a “critical” or “extremely critical” condition.

IS had first claimed responsibility for the attack on Friday night, before repeating its claim on Saturday and then publishing a graphic video of the gunmen carrying out the attack.

After walking through the theatre and shooting spectators, they set fire to the building, Russian investigators said, trapping many inside who died from smoke inhalation.