US intel warns of potential terrorist threat at gatherings after Moscow attack

Law enforcement officials expressed concern that radicals in the U.S. might respond to ISIS calls for similar attacks in the wake of last month's deadly terrorist attack at a concert hall in Moscow.

The U.S. intelligence bulletin warns that ISIS operatives worldwide and so-called "lone wolves" might respond to recent statements from the terrorist group touting the attack in Russia and encouraging more attacks on public venues -- even if the individuals are not members of ISIS.

Russian investigators said the March 22 attack in Moscow's Crocus City Hall killed at least 144 people, including three children, and injured at least 550 others. Nine suspects -- identified as citizens of Tajikistan -- were arrested after gunmen opened fire on concertgoers with automatic weapons and then set a fire that engulfed the complex, according to Russian authorities.

ISIS released a statement after the attack, claiming their fighters "attacked" a "big gathering for Christians in the Russian Moscow suburb."

The U.S. said it shared intelligence with Russia that warned that ISIS was preparing similar attacks on concerts in Moscow weeks before the attack. A State Department official said that the U.S. government had shared information on a possible attack with Russian authorities in accordance with its longstanding "duty to warn" policy.

The U.S. Embassy in Moscow issued a warning on March 7, advising U.S. citizens to avoid large gatherings for 48 hours, saying extremists have "imminent plans" to target large-scale gatherings in Moscow.