At least 133 people were killed and dozens were injured when gunmen stormed a concert hall in a Moscow suburb on Friday, Russia's Investigative Committee said, while Tass news agency said four people suspected of direct involvement were detained.
The attack by several people clad in fatigues at Crocus City Hall, where explosions and a fire were reported, prompted the country's federal authorities to launch a terrorism investigation, according to media reports.
Islamic State claimed responsibility for the attack through a news agency affiliated with the militant group. A U.S. official said the United States had intelligence confirming the claim, the reports said.
Interfax news agency said up to five people were involved in the attack, in which weapons including hand grenades were used against concertgoers awaiting the start of a show.
Images posted on social media appeared to show several people with backpacks storming the concert hall from the main entrance and shooting automatic rifles.
Ukrainian presidential adviser Mykhailo Podolyak denied Kyiv was involved in the incident, saying on the X social media platform, "Ukraine certainly has nothing to do with the shooting/explosions in the Crocus City Hall."
In Washington, White House national security spokesman John Kirby told reporters, "There is no indication at this time that Ukraine or Ukrainians were involved in the shooting."
The complex housing the city hall was ablaze after the explosions and dozens of fire trucks were at the scene. Police and security forces searched for the attackers around the area.
Earlier this month, the British Foreign Office and the U.S. Embassy in Moscow urged their nationals in Russia to avoid crowds, citing the possibility of terrorist attacks.
