An explosion near the Balzi Rossi restaurant in Moscow’s Kudrinskaya Square killed at least three people and injured 21, Russian authorities said. The blast occurred at about 8 p.m. local time on Saturday near the entrance to the restaurant, located on the ground floor of a Stalin-era high-rise building.

Russia’s Interior Ministry said on the social media platform Max that the explosion came from a hand grenade or improvised explosive device carried by a woman. The National Anti-Terrorism Committee said she was stopped by a security guard while trying to enter the restaurant, and the device exploded at that point. It said those killed included the guard, the woman and a restaurant guest, though the account could not be independently verified.

Police initially reported three deaths and 15 injuries before the number of injured was updated to 21. Armed security forces cordoned off the area and barred public access to the restaurant. Authorities rejected early speculation of a gas-cylinder explosion and described the incident as an attack. They have not released the identities of those killed or injured, or named any additional suspects.