The victim believed to have been the target of the attack is described in Russian media as a former boxer from eastern Ukraine who set up a paramilitary battalion and joined the Russian side in the Ukraine war. The man is said to have been seriously injured in the explosion and later died in hospital.
Even the man's bodyguard was killed, and several other people were injured, according to USA-supported Radio Free Europe/Radio Liberty. The blast was caused by a homemade bomb or a grenade, reports the media site Meduza.
Images on social media show ongoing rescue efforts in a room filled with shattered glass. The state-controlled news agency Tass reports that the ceiling in the entrance was damaged, but there is no reported danger to the building as a whole.
"There was a big blast in the lobby of the Scarlet Sails facility. Windows and plaster ceilings have been damaged," says a source to Tass.
Scarlet Sails, or Alje Perusa, is described as a large-scale residential complex with many floors, named after an annual summer festival with millions of visitors in St. Petersburg.
