A group of gunmen stormed a concert venue on the outskirts of Moscow on Friday night, killing at least 40 people and wounding more than 100, Russia’s top security agency said, according to state news agencies.

The authorities in Russia have yet to identify who was behind the attack, and no group has claimed responsibility.

The assault also led to to an enormous fire at the venue, Crocus City Hall, which is one of the largest and most popular concert halls in Moscow and the site of a shopping mall.

State media agencies reported that there were up to five perpetrators, and Russia’s Investigative Committee, the country’s equivalent to the F.B.I., said it had opened a criminal case into a terrorist act.

Mykhailo Podolyak, a top adviser to Ukraine’s presidential office, said in a video statement that “Ukraine has absolutely nothing to do” with the attack.

On March 7, the U.S. Embassy in Moscow issued a security alert warning that its personnel were “monitoring reports that extremists have imminent plans to target large gatherings in Moscow, to include concerts.”

Below, a body in the parking lot outside the concert hall after the attack.

Firefighters worked on putting out the blaze at the concert hall.

A still image taken from a video obtained by Reuters shows gunmen walking through the concert hall and firing on people.

Security personnel directed people outside the concert hall.

A Russian national guard officer in the parking lot after the assault.

A police officer shouting outside.

A couple walked through the parking lot after the attack.