The death toll in the terror attack at Moscow's Crocus City Hall has risen to 137 people, including three children, Russia's Investigative Committee said Sunday, as the search operation continues for bodies under the rubble.
Russian President Vladimir Putin was informed Saturday that four suspected gunmen responsible for the attack were arrested near Russia's western border with Ukraine, Russian news agencies reported.
Seven others have been detained and the search for other accomplices is ongoing, the state news outlets reported.
ISIS claimed responsibility for the deadly attack Friday night, in which gunmen opened fire on concertgoers at one of Moscow's largest entertainment complexes. The attackers then set the complex on fire.
Earlier, Russian media posted unverified photos of a car they said belonged to some of the attackers near Russia's western border, and a Russian MP said at least two suspects were detained after a car chase and a shootout, though neither of these has been verified or confirmed by Russian authorities.
The death toll as a result of the terrorist attack has increased to 137, Russian investigators said Sunday, adding that three of the victims are children. The search for bodies under the rubble of the complex continues. Authorities said earlier that the toll could rise significantly. The local governor said 121 people remain hospitalized.
Investigators said more than 500 rounds of ammunition and 28 magazines, as well as two Kalashnikov assault rifles, were found at the scene.
Preliminary data shows the causes of death were gunshot wounds and poisoning by smoke products, according to a statement from the Investigative Committee.
"The terrorists used automatic weapons during the attack, which, along with the ammunition they left behind, were discovered and seized by the investigators," it added.
"The terrorists also used flammable liquid to set fire to the premises of the concert hall, where there were spectators, including the wounded," the statement said.
Putin spoke out publicly for the first time about the attack on Saturday, promising to exact "retribution" on anyone involved in it.
Putin did not acknowledge the ISIS claim for the attack, saying Russia was still investigating. But he sought to suggest that Ukraine could bear some responsibility, saying the suspected attackers had been detained while trying to cross the border to Ukraine and claiming they may have received some help from there.
"According to the preliminary data, they had a crossing of the border prepared from the Ukrainian side," Putin said.
Ukrainian officials vehemently denied any involvement and warned that the Kremlin would try to exploit the attack by falsely blaming Ukraine to drum up greater support for its war.
Putin's comments followed several statements by some leading Kremlin figures directly accusing Ukraine and Western countries of being behind the attack, despite the ISIS claim.
The U.S. said it shared intelligence with Russia that warned that ISIS was preparing similar attacks on concerts in Moscow just two weeks ago. A U.S. State Department official said Saturday that the U.S. government had shared information on a possible attack with Russian authorities in accordance with its longstanding "duty to warn" policy.
The U.S. Embassy in Moscow issued a warning on March 7, advising U.S. citizens to avoid large gatherings for 48 hours, saying extremists have "imminent plans" to target large-scale gatherings in Moscow.
"The United States strongly condemns yesterday's deadly terrorist attack in Moscow," Secretary of State Antony Blinken said in a statement Saturday. "We send our deepest condolences to the families and loved ones of those killed and all affected by this heinous crime. We condemn terrorism in all its forms and stand in solidarity with the people of Russia in grieving the loss of life from this horrific event."
Ambassador to the United States Anatoly Antonov said the U.S. didn't pass along any "concrete information" prior to the attack.
"Nothing was passed," Antonov told Russian state news agency TASS while answering a question about whether any information was handed over by the U.S. side before the terrorist act.
He added, "No concrete information, nothing was transferred to us."