Putin vows retribution for Moscow concert hall attack

Russian President Vladimir Putin on Saturday vowed to punish those behind a "barbaric terrorist attack" on a Moscow concert hall that killed more than 130, saying Russia had arrested four gunmen who were trying to flee to Ukraine.

Kyiv has strongly denied any connection, and Putin made no reference to claims of responsibility by the Daesh group in his first public remarks on the attack.

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.

The militant group has claimed the attack, writing on Saturday on a Telegram channel that it was "carried out by four Daesh fighters armed with machine guns, a pistol, knives and firebombs", as part of "the raging war" with "countries fighting Islam".

It is the deadliest attack in Russia for almost two decades and the deadliest in Europe to have been claimed by Daesh.

Russian officials expect the death toll to rise further, with more than 100 injured in hospital.

"Terrorists, murderers, non-humans ... have only one unenviable fate: Retribution and oblivion," Putin said in a televised address to the nation on Saturday.

Calling the attack a "barbaric, terrorist act", he said "all four direct perpetrators ... all those who shot and killed people, have been found and detained".

"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," he added.

Putin also compared the attackers to "Nazis" and said the attack was an "atrocity, a strike against Russia and our people".

He named Sunday a day of national mourning.

Russia arrested 11 people in connection with the attack on Saturday, the FSB security service said.

"All the perpetrators, organisers and those who ordered this crime will be justly and inevitably punished," Putin said.

The FSB said earlier that the assailants had "contacts" in Ukraine, without providing further details.

Kyiv, facing a Russian military offensive for the past two years, had "nothing to do" with the attack, presidential aide Mykhailo Podolyak said in a statement.

Poland's Prime Minister Donald Tusk said Saturday he hoped "this terrible tragedy will not become a pretext for anyone to escalate violence and aggression."

Russia's Investigative Committee, which probes major crimes, said rescue workers were still pulling bodies from the burnt-out building on Saturday.

"The emergency services have found more bodies while clearing the debris," it said in a statement on Telegram.

"The number of people killed in the terrorist attack has risen to 133. Search operations continue."

The governor of the Moscow region said rescuers would continue to scour the site for "several days."

Some 107 people were still in hospital, many in a critical condition, Deputy Prime Minister Tatyana Golikova said.

Daesh had first claimed responsibility for the attack on Friday night, repeating its claim again on Saturday.

Some witnesses filmed the gunmen from the upper floors as they walked through the stalls shooting people, footage shared on social media showed.

Then "the terrorists used a flammable liquid to set fire to the concert hall's premises, where spectators were located, including wounded," the Investigative Committee said.

Investigators said people died both from gunshot wounds and smoke inhalation after a fire engulfed the 6,000-seater venue.

Flames quickly spread through the venue on Friday, with screaming concert-goers rushing to emergency exits.

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