The alarm about the explosion came at around 10.30 pm on Tuesday evening after a loud bang was heard in a residential area in southern Stockholm.
Pictures from the scene show how an entrance door was damaged by an explosion and information to SVT claims that it was a hand grenade that detonated in a stairwell.
National bomb protection
The National Bomb Squad has been called to the scene and police technicians will now carry out a technical investigation.
There is currently no information that anyone was injured in connection with the explosion. The police are investigating the incident as public vandalism, but have not yet made any arrests.
The article is updated.