Suspects arrested after Moscow concert hall attack leaves at least 115 dead; ISIS claims responsibility

State media reported Saturday that Russian authorities detained 11 people — including four suspected gunmen — for their involvement in a deadly attack on a crowded concert hall near Moscow on Friday that has left at least 115 people dead.

The attack left hundreds more injured, Russian officials said.  

The four suspects were stopped in the Bryansk region of western Russia, “not far from the border with Ukraine,” Russia’s Investigative Committee said. They planned to cross the border into Ukraine and “had contacts” there, state news agency Tass said, citing Russia’s FSB. The head of the FSB briefed President Vladimir Putin on the arrests on Saturday, according to Tass.

Videos circulated on Russian social media show pandemonium inside the large concert hall, which is connected to a shopping mall. Videos show people screaming and ducking for cover as gunmen fire volley after volley of automatic gunfire. Other clips show the gunmen firing, sometimes at point-blank range. The attackers also set the venue on fire, causing a partial collapse of the building’s roof. 

“The shots were constant,” eyewitness Dave Primov told CBS News. “People panicked and started to run. Some fell down and were trampled on.” 

The Islamic State group has claimed responsibility for the attack. A U.S. official told CBS News that the U.S. has intelligence confirming the Islamic State’s claims of responsibility, and that they have no reason to doubt those claims. 

The U.S. Embassy in Russia had previously advised Americans to stay away from concert venues, citing the threat of a terrorist attack. The U.S. official confirmed that the U.S. provided intelligence to Russia about a potential attack under the intelligence community’s Duty to Warn requirement. A U.S. law enforcement official told CBS News that there is no known threat to the U.S. emanating from the Moscow attack.

The attack came just days after Putin cemented his grip on power in a highly orchestrated electoral landslide amid the country’s war with Ukraine. 

On Friday, the U.N. Security Council condemned “the heinous and cowardly terrorist attack” and underlined the need for the perpetrators to be held accountable. U.N. Secretary-General Antonio Guterres also condemned the terrorist attack “in the strongest possible terms,” his spokesman said.

Meanwhile, in Moscow, hundreds of people stood in line Saturday morning to donate blood and plasma, Russia’s health ministry said.

This is the most deadly terror attack in Russia in years. The country was shaken by a series of deadly terror attacks in the early 2000s during the fighting with separatists in the Russian province of Chechnya.

In October 2002, Chechen militants took about 800 people hostage at a Moscow theater. Two days later, Russian special forces stormed the building, and 129 hostages and 41 Chechen fighters died, most of them from the effects of narcotic gas Russian forces used to subdue the attackers.

And in September 2004, about 30 Chechen militants seized a school in Beslan in southern Russia, taking hundreds of hostages. The siege ended in a bloodbath two days later and more than 330 people, about half of them children, were killed.

CBS News’ Debora Patta, David Martin, Andy Triay and Olivia Gazis contributed to this report.