At least 40 people were killed and 145 wounded on Friday when camouflage-clad gunmen fired with automatic weapons on concertgoers near Moscow in one of the deadliest attacks on Russia in decades.
Islamic State, the militant group that once sought control over swaths of Iraq and Syria, claimed responsibility for the attack, the group's Telegram channel said.
The United States has intelligence confirming Islamic State's claim of responsibility for the shooting, a U.S. official said on Friday. The official said Washington had warned Moscow in recent weeks of the possibility of an attack.
"We did warn the Russians appropriately," said the official, speaking on condition of anonymity, without providing any additional details.