Several camouflage-clad gunmen opened fire today at a popular concert hall on the outskirts of Moscow, killing at least 40 people and wounding more than 100, Russia’s top security agency said, according to state news agencies. Here’s the latest.

More than a third of the venue, which was set to hold a sold-out performance by the rock band Piknik, caught on fire. Emergency services tried to rescue people from the roof, which was collapsing, according to a state news agency.

There was no report of who might be responsible for the attack, but state media said that there were up to five perpetrators. The attack at the concert venue, Crocus City Hall, in the suburb of Krasnogorsk, could be the deadliest in Russia in decades.

In videos filmed inside the hall, audience members are heard screaming, and there are multiple gunshots. Other videos filmed from a highway outside of the building show parts of it on fire producing heavy smoke.

A White House official said there was no indication that Ukraine was involved. On March 7, the U.S. Embassy in Moscow issued an alert warning of a possible attack by “extremists.”

Russian authorities said they had opened a criminal investigation into a terrorist act and dispatched investigators. Russia tightly regulates firearm possession and mass shootings are rare.