Assailants opened fire at a large concert hall in Moscow on Friday, killing more than 60 people, injuring more than 100 others, and setting fire to the venue.
The Islamic State group claimed responsibility for the attack in a statement on the group's Telegram channel.
In a statement posted by its Aamaq news agency, the group said it attacked a large gathering of Christians in Krasnogorsk on Moscow's outskirts, killing and wounding hundreds.
On Friday, several gunmen dressed in camouflage burst into the Crocus City Hall, a 6,200-seat venue on the Western edge of Moscow, according to witnesses and social media posts.
Video posted on social media show people rushing for the exits as repeated volleys of gunfire are heard. Other videos show men with rifles moving through the venue and shooting people at point-blank range.
The assailants also threw explosives, setting off a huge fire at the complex.
Video from outside the building showed helicopters flying overhead to dump water on the blaze. Media reports said the roof of the building had partially collapsed.
Russia's Federal Security Service put the death toll from the attack at more than 60 people. Russian health authorities released a list of 145 injured - 115 of them hospitalized.
US warned of extremists
The United States collected intelligence earlier this month about a planned terrorist attack in Moscow, potentially targeting large gatherings. The U.S. government "shared this information with Russian authorities in accordance with its longstanding 'duty to warn' policy," Adrienne Watson, National Security Council spokesperson, said in a statement Friday night.
The U.S. embassy also issued a warning earlier this month that "extremists" had imminent plans for an attack in Moscow. Those warnings were repeated by other Western embassies and came hours after Russia's top security agency said it foiled an attack the Islamic State group was preparing for a Moscow synagogue.
The New York Times reported Friday that the U.S. intelligence specifically involved Islamic State-Khorasan, known as ISIS-K, the branch of the group based in Afghanistan. ISIS members have been active in Russia, one U.S. official told the paper.
Moscow mayor cancels gatherings
Friday's attack came just days after Russian President Vladimir Putin won reelection in polls in which he faced no effective opposition due to the intimidation or jailing of most potential opponents.
The Kremlin said Putin was informed about the attack minutes after it began.
"The president constantly receives information about what is happening and about the measures being taken through all relevant services. The head of state gave all the necessary instructions," Kremlin spokesperson Dmitry Peskov said.
Following the attack, Moscow's mayor canceled all large gatherings and ordered theaters and museums to close for the weekend. Large-scale events were also canceled across the country.
It is not clear what happened to the assailants after the attack.
The Islamic State group said its fighters carried out an attack on the outskirts of Moscow, "killing and wounding hundreds and causing great destruction to the place before they withdrew to their bases safely." The statement gave no further details.
Islamic State operates mainly in Syria and Iraq, but also in Afghanistan and parts of Africa.
