Editor's note: This is a developing story and is being updated.
Several gunmen opened fire at a concert hall in Krasnogorsk, northwest of Moscow, on the evening of March 22, killing and injuring dozens of people, Russian media claimed.
Kremlin-controlled media RIA Novosti claimed that at least three men sporting camouflage and automatic weapons shot at people at the Crocus City Hall ahead of a concert.
The terrorist group Islamic State (IS) claimed responsibility for the shooting in a Telegram post shortly after the attack. U.S. intelligence officials confirmed the claim.
More than 60 people were killed in the attack, Russia's Investigative Committee reported.
Russian officials reported that over 140 people were injured in the shooting, with 115 requiring hospitalization.
Members of Russia's National Guard arrived at the scene, according to TASS. More than 50 ambulances were reportedly sent to the concert venue.
Several Russian outlets also reported explosions, causing the building's roof to start collapsing.
FSB said it is taking "all necessary measures" in connection with the shooting.
Kremlin spokesperson Dmitry Peskov said that Russian President Vladimir Putin was informed about the shooting "in the first minutes of the incident," according to TASS.
U.S. National Security Council spokesperson John Kirby said that images of the shooting in Moscow were "horrible and just hard to watch." He emphasized that there is no indication at this time "that Ukraine, or Ukrainians, were involved in the shooting," AFP reported.
Andriy Yusov, spokesperson of Ukraine's military intelligence agency (HUR), called the shooting "a deliberate provocation of the Putin regime, which the international community has warned about."
On March 7, the U.S. Embassy in Russia issued a warning that "extremists have imminent plans to target large gatherings in Moscow" and urged American citizens to stay away from crowded areas and venues over the next 48 hours. U.K., Canada, Germany and several other countries published similar statements soon after this.
"The Kremlin tyrant started his career with this and wants to end it with the same crimes against his own citizens," Yusov told Ukrainska Pravda.
Advisor to Ukraine's Presidential Office head Mykhailo Podolyak said "Ukraine is definitely not involved in these events."
In a post on its Telegram channel, HUR claimed the shooting is intended to justify "even tougher" attacks on Ukraine and total mobilization in Russia.
"The unimpeded movement of a group of militants with assault rifles through the center of Moscow, as well as a lot of other indisputable evidence, indicate that the shooting in Crocus City Hall was organized by the Russian special services," Ukrainian military Intelligence wrote.
In 1999 shortly after Putin become president, a series of apartment bombings rocked Russia which were blamed on Chechen separatists, lighting the fuse for the second Chechen war.
Since then, speculation has continued that Putin and Russia's Federal Security Service (FSB) orchestrated the bombings to boost his popularity and legitimize the war.