By Heather Chen, Andrew Raine, Catherine Nicholls, Antoinette Radford, Maureen Chowdhury and Kathleen Magramo, CNN
Russia is observing a day of mourning for the more than 130 victims of the attack on a Moscow concert hall on Friday.
President Vladimir Putin declared Sunday a day of national mourning, vowing to punish the perpetrators and expressing condolences to those who had lost loved ones.
"The whole country, our whole people, mourns with you," he said. The attack is Russia's deadliest in two decades.
From CNN staff
A Friday night attack at Crocus City Hall, a popular concert venue complex near Moscow, left more than 130 people killed and even more wounded after assailants stormed the venue with guns and incendiary devices. ISIS has claimed responsibility for the attack, without providing evidence.
Four suspects involved in the attack were detained in the Bryansk region and taken to Moscow, where they are now in the custody of Russia's Investigative Committee, Russian state media TASS reported Saturday.
Ukrainian President Volodymyr Zelensky said "miserable" Russian President Vladimir Putin waited overnight before publicly addressing Russians, only to accuse Ukraine of having a hand in the terror attack at a concert hall near Moscow.
Here are other headlines you should know:
From CNN’s Sophie Jeong and Manveena Suri
North Korean leader Kim Jong Un has offered his condolences to Russian President Vladimir Putin following the deadly concert attack in Moscow, state media Korean Central News Agency (KCNA) reported on Sunday.
Kim “expressed deep condolences and sympathy” to Putin, the Russian people, the victims and their families on the news of heavy casualties caused by a “large-scale terrorist attack in (the) Moscow region,” KCNA reported.
North Korea opposes “all sorts of terrorism and nothing can justify the heinous terrorism threatening human life,” Kim said in the KCNA report. “Our people regard the misfortune and sorrow of the friendly Russian people as their own pain.”
From CNN's Kareem El Damanhoury and Paul Murphy
ISIS-affiliated news agency Amaq released a graphic video on Saturday that purports to show Friday’s attack at a concert hall in suburban Moscow recorded by one of the attackers, suggesting the perpetrators had a direct link to ISIS in order to be able to send the video.
CNN has geolocated it to the concert hall and notes that its identifying metadata has been erased.
The video, which is about 90 seconds long, shows four attackers with their faces blurred and voices distorted in what appears to be the Crocus City Hall complex.
The video shows one attacker signaling to another gunman, who then walks past a door where people are hiding and opens fire on them.
Bodies and blood can be seen on the floor, with fire raging at a distance.
The video also shows one of the attackers slitting the throat of a man lying on his back.
The video ends with the four attackers walking away inside the building as smoke can be seen at a distance.
On Friday, ISIS claimed responsibility for the attack, according to a short statement published by Amaq.
On Saturday, Russian President Vladimir Putin suggested Ukraine was behind the attack, stating the perpetrators had “tried to hide and moved towards Ukraine, where, according to preliminary data, a window was prepared for them on the Ukrainian side to cross the border.”
Ukraine has vehemently denied any connection to Friday's attack.
From CNN's Natasha Bertrand and Samantha Waldenberg
US Vice President Kamala Harris and the White House National Security Council said there is no evidence that Ukraine is behind the attack at a concert hall near Moscow.
“There is no, whatsoever, any evidence — and in fact, what we know to be the case is that ISIS-K is actually, by all accounts, responsible for what happened,” Harris said in an interview with ABC News. “What has happened is an act of terrorism and the number of people who've been killed is obviously a tragedy and we should all send our condolences to those families."
National Security Council spokesperson Adrienne Watson said:
"In early March, the US government shared information with Russia about a planned terrorist attack in Moscow. We also issued a public advisory to Americans in Russia on March 7. ISIS bears sole responsibility for this attack. There was no Ukrainian involvement whatsoever."
From CNN's Maria Kostenko
Ukrainian President Volodymyr Zelensky said "miserable" Russian President Vladimir Putin waited overnight before publicly addressing Russians, only to accuse Ukraine of having a hand in the terror attack at a concert hall near Moscow.
On Saturday, Putin told the Russian people that the perpetrators of the Crocus City Hall attack had “tried to hide and moved towards Ukraine, where, according to preliminary data, a window was prepared for them on the Ukrainian side to cross the border.”
Zelensky and several Ukrainian officials have vehemently denied Ukraine has any kind of involvement in the attack.
In his nightly address, Zelensky also said that Russians "have come to Ukraine, burn our cities – and try to blame Ukraine."
Zelensky added that if the Russian people do "not ask any questions to their security and intelligence agencies, then Putin will try to turn such a situation to his personal advantage again."
More background: The terror group ISIS claimed responsibility for Russia's attack, according to a short statement published by ISIS-affiliated news agency Amaq on Telegram Friday. ISIS has not provided evidence to support the claim.
Earlier this week, Putin had dismissed warnings by the US embassy that there could be terrorist attacks on large groups, telling the Federal Security Service (FSB) that the embassy warnings were "provocative" and "outright blackmail."
From CNN's Masha Angelova
Four suspects in Friday's terrorist attack on Crocus City Hall were detained in the Bryansk region and taken to Moscow, where they are now in the custody of Russia's Investigative Committee, Russian state media TASS reported Saturday.
The suspects were brought in two prisoner transport vehicles, which are still in the courtyard of the committee, a TASS correspondent reported. This indicates that the suspects are being interrogated and the investigation is ongoing, according to TASS.
In the coming days, investigators are expected to file a court motion asking for imprisonment as the chosen preventative measure. All four suspects face life imprisonment, TASS reports.
Analysis from CNN Chief International Security Correspondent Nick Paton Walsh
Gunmen in an entertainment venue. Bodies lying on the cold concrete. Horror that such murder could strike the safety of the Moscow bubble.
These were all present in the horrific aftermath of Friday night’s savage attack outside Crocus City Hall just as they were almost 22 years ago when I was outside the Dubrovka Theatre, where Chechen gunmen took 800 hostages, and a standoff ended with a special forces raid.
While the theatre attacks of 2002 marked just one of many horrific low points in Russian President Vladimir Putin’s war on Islamist extremism, last night showed that the brutal past has come back to haunt the Kremlin – if, indeed, it ever left.
Yet Putin faces the same sort of Islamist enemy as 2002, in a world transformed. If indeed ISIS-K – the militant group’s Afghan branch – were responsible, as their claim and advance warnings from US officials suggest, it means a new generation of extremists have Russia in their sights, following Russia’s bloody suppression of Islamism in the south.
From CNN’s Eve Brennan
Anastasia Rodionova, a survivor of the Moscow region's Crocus City Hall attack, told Reuters Saturday that the armed assailants were "gunning down everyone methodically in silence" inside the venue on Friday night.
“They did not shoot upwards, they did not scream, they did not say, 'Everyone lay down, we will kill you,' and etc. They were just walking and gunning down everyone methodically in silence. The sound was echoing and we could not understand what was where,” she said.
"It is unbelievable. You understand only now that you are lucky, really lucky. I came home; my coat was just covered in blood,” she added.
Another survivor of the attack, Margarita, who did not provide her last name, told Reuters that “the gunshots were going on and on.”
“We went down to some kind of ground floor, some dark room, and I saw only 'exit' word shining in the darkness, and we just did not know whether to run or not. Who is there in the dark? What is there in the dark?” she said.
"We were very distressed yesterday, of course it is very hard. Because we came home yesterday ... and an ambulance came, and they gave a sedative drug ... and you close your eyes and you see it, when you are left alone, you hear that. And today I express my condolences to everyone. It is a misfortune, it is a grief,” she added.
