STRINGER / AFP
Russia will observe a national day of mourning on Sunday after a massacre in a Moscow concert hall on Friday that killed more than 130 people.
President Vladimir Putin has vowed to punish those behind the "barbaric terrorist attack", saying four gunmen trying to flee to Ukraine had been arrested.
Kyiv has strongly denied any connection, with Ukrainian President Volodymyr Zelensky accusing Putin of trying to shift the blame onto them.
Putin, in his first public remarks on the attack, did not refer to a statement by ISIS claiming responsibility.
At least 133 people were killed when camouflaged gunmen stormed the Crocus City Hall, in Moscow's northern suburb of Krasnogorsk, and then set fire to the building on Friday evening.
On Saturday, the Islamic State group wrote on social media that the attack was "carried out by four IS fighters armed with machine guns, a pistol, knives and firebombs," as part of "the raging war" with "countries fighting Islam".
It was the deadliest attack in Russia for almost two decades.
Russian officials expect the death toll to rise further, with more than 100 wounded in hospital.
The country's Investigative Committee, which probes major crimes, said rescue workers were still pulling bodies from the burnt-out building on Saturday.
