Aug. 2 (UPI) — The mayor of Moscow on Sunday called a deadly restaurant bombing in his city a day earlier a “terrorist attack.”

Three people were killed and 21 injured when a woman carrying a package attempted to enter the upscale Italian restaurant Balzi Ross carrying a package.

The box exploded, killing the woman, a security guard and a bystander.

“Yesterday, a brutal terrorist attack took the lives of people in Moscow,” Mayor Sergei Sobyanin said in a statement on Telegram. “The victims are currently in city hospitals, where they are receiving all necessary care.”

The mayor said law enforcement officials are still investigating the event, and offered no details on motive.

“Those responsible for this crime will certainly be found and brought to justice,” Sobyanin added.

Preliminary reports indicate the woman was a courier and likely didn’t know the package’s contents, Kommersant reported.

Investigators believe the bomb could have been detonated remotely, the newspaper added.

“When I left the building, I saw smartly dressed women running out of the restaurant,” one eyewitness told Kommersant. “They were carrying their shoes, followed by a shirtless man with a bloody T-shirt.”

The restaurant, located in central Moscow’s Kudrinskaya Square, had been closed for a private banquet.