UPDATE 3/23: The death toll from the attack has risen to at least 133, and Russia has detained 11 suspects, including four who were directly involved in the attack, The Associated Press reports. The Islamic State group claimed responsibility in a statement, and a US intelligence official confirmed to the AP that the group. was behind the attack, but Russian agencies seemed to suggest the attack was linked to Ukraine. Russian agencies said the suspects were apprehended near the Ukraine border and that they “had contacts” there.

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At least 40 people are dead after a mass shooting outside a Moscow concert venue, the New York Times reports.

At least three gunmen in camouflage burst into the ground floor of Crocus City Hall on the outskirts of Moscow and opened fire with automatic weapons during a concert by the band Piknik. More than a third of the 6,000-capacity venue was on fire during the shooting, according to the Russian news agency TASS. It’s Russia’s deadliest attack in decades. More than 100 others were wounded in the attacks. Videos from the site showed massive plumes of smoke rising up.

Piknik issued the following statement on Instagram: “Today a tragedy occurred in Crocus City Hall, the scale of which we cannot yet estimate. We are following the news in anticipation of official information. The band’s musicians and management are alive and safe.” Moscow Mayor Sergei S. Sobyanin called it a “terrible tragedy.”

The attack is being investigated as terrorism. Tuesday, the US Embassy in Russia issued a warning about a possible terrorist attack, which Russian President Vladimir Putin dismissed as “obvious blackmail.”