MOSCOW - 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 Islamic State group (IS) 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 jihadist group has claimed the attack, writing Saturday on a Telegram channel that it 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".
It is the deadliest attack in Russia for almost two decades and the deadliest in Europe to have been claimed by IS.
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.
- 'Barbaric' -
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."
- At least 133 killed -
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.
IS 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.
Investigators also said they would issue an award to a man who had jumped on one of the attackers while he was shooting at the concert-goers, "immobilising" the gunman and "saving the lives of people around him".
- Blood queues -
Putin did not address IS's claim of responsibility in his first public remarks on Saturday, which came more than 18 hours after the start of the attack.
The head of the state-run RT media outlet, Margarita Simonyan posted two videos claiming to be interrogations of two handcuffed suspects, who both admitted to the attack but did not say who organised it.
The interior ministry said all four of the suspected gunmen were foreign nationals, as Russian Telegram channels -- including those with links to the security services -- said they were from Tajikistan, a country that borders Afghanistan and where the jihadist group is active.
Tajikistan's foreign ministry told Russia's TASS news agency that authorities were "in close contact" with Moscow about the "supposed participation of the country's citizens in the terrorist attack".
In Moscow, residents stood in long lines in the rain to donate blood for those hospitalised, and mourners came to lay flowers outside the concert hall.
Memorial posters featuring a single candle replaced some advertising billboards in the capital.
Major events were cancelled across the country, including a friendly football match between Russia and Paraguay set to take place in Moscow on Monday.
Statements of condemnation from world leaders continued to roll in.
- US warning dismissed -
Russia's powerful intelligence services were also in the spotlight in the wake of the attack.
The US embassy in Russia had warned on 7 March that "extremists have imminent plans to target large gatherings in Moscow, to include concerts".
Washington said after the attack it had also shared details directly with Moscow.
But speaking to FSB chiefs last Tuesday, Putin had called it a "provocative" statement and "outright blackmail... to intimidate and destabilise our society".
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