Three people were killed and 21 injured after an improvised bomb was detonated at a restaurant in central Moscow, Russia’s National Anti-Terrorism Committee Information Center told the state news agency TASS.

At 7:55 p.m., “a homemade explosive device detonated in a restaurant on Kudrinskaya Square in Moscow, killing three people: a security guard who prevented an unknown woman suspected of attempting to smuggle an explosive device from entering the restaurant, the unknown woman herself, and one of the patrons,” the National Anti-Terrorism Committee said, according to TASS.

Russia’s Investigative Committee, the country’s equivalent of the F.B.I., has launched a terrorism investigation.

The upscale restaurant, Balzi Rossi, sits in a very central area of Moscow, just off the Garden Ring, in a Stalin-era skyscraper. The restaurant’s website said it had been closed on Aug. 1 for a private party.

The restaurant’s chef, Carmine Alfieri, wrote a post on Instagram that was later deleted that “we are fine, our restaurant and our kitchen are in perfect condition,” after rumors circulated that it could have been a gas leak.

Photos and videos in local news outlets showed the area around the restaurant cordoned off, with ambulances parked nearby.